A quick, simple glossary of common Search Engine Optimisation (SEO) acronyms, terms, and phrases.


An advertisement programme by Google, allowing publishers to serve advertisements across the Web. AdSense supports text, image and video advertisements.


Another advertisement programme by Google, AdWords allows advertisers to publish ads within Google’s ad network, for instance in Google Search results.

Alt Attribute

An attribute used in HTML, typically images, to specify “alternative text” which is only displayed if the element cannot be rendered. For instance, an image of a car may have the alt text “Image of a blue Ford Focus” which is shown to users if the image fails to load in their browser. Alt tags are especially useful for users with limited vision who rely on screenreaders to browse the Web.


Short for Cascading Style Sheets, CSS is a style sheet language that is used to style the Web.


Click-through Rate (CTR) is the ratio of users who click on a link to those who have visited a Web page. In SEO, CTR is a very useful metric, often used to measure the success of an SEO or advertising campaign.


A cookie is a small text file that is stored on a user’s computer by their web browser, when the user visits a website. Cookies are used to store the user’s settings, login details, and other information, so the website can identify the user when they visit later.

Cookie stuffing

Cookie stuffing is a technique used by affiliate marketers to include a third-party cookie from an affiliate site, within the unrelated site the user is visiting. For instance, an Amazon Affiliate marketer running CoolWebsite.com may include a 3rd-party cookie from Amazon within their website, as if the user had visited Amazon.com. Cookie stuffing is a negative practice and is forbidden by the vast majority of affiliate services, and can lead to suspension from the service.


The Domain Name Service (DNS) is the protocol responsible for translating IP addresses into domain names. It’s the “phone book” of the Internet. For example, when you connect to Google.com, the DNS service of your ISP handles finding the appropriate domain name (Google.com) from the IP address Google’s web server uses (e.g.

Dead link

A dead link, also known as a broken link, is a link to a page or resource that is permanently unavailable. Dead links contribute to link rot, whereby pages that are not frequently updated are gradually filled with dead links. Dead links are often the result of content being moved around or removed, resulting in 404s, or the result of websites that have ceased to exist.

From an SEO perspective, dead links are a negative thing; it’s important to avoid dead links by frequently updating pages to ensure content linked is available and relevant.


Earnings Per Click (EPC) refers to the earnings received, on average, each time a user clicks on an advertisement.

For example, if an offer shows $0.50 EPC, you will make 50 cents each time an advertisement is clicked by a user.

EPC is sometimes referred to as visitor value.


A website referred to as a Free-For-All (FFA) is one that allows any user to submit a link to their website, and contains many such links. FFA websites are commonly utilised under the false assumption they can improve SEO; this is not true. Search engines such as Google look negatively on websites linked on FFA pages, and may penalise a website if it is found on multiple FFA pages.


File Transfer Protocol (FTP) is used to transfer files to and from servers.


Hypertext Markup Language (HTML) is used to structure web pages; pages are made up of many HTML elements such as paragraph tags (<p>), divider tags (<div>), image tags (<img>), and hundreds of other types.

You can read more about HTML and learn how to write HTML on Mozilla’s Development Network: https://developer.mozilla.org/en-US/docs/Learn/HTML

Although many modern web hosts provide drag-and-drop functionality, and Content Management Systems (CMS) such as WordPress allow WYSIWYG editing, HTML is relatively easy to learn, and even a limited knowledge of HTML is very useful to have.


Hypertext Transfer Protocol, or HTTP, is fundamental to the modern Web. It is the protocol used to allow communication between users (browsers) and servers (websites) over the Web.


Put simply, Inverse Document Frequency (IDF) is a measure of a keyword’s uniqueness. The higher the IDF score, the less frequently a keyword appears, and thus the keyword is rarer or more unique.

Popular keywords, such as “football”, “shopping” and “televisions” are highly competitive keywords from an SEO perspective; there are millions of websites fighting over these keywords, because they are extremely common, and so have a low IDF score.

When considering SEO, it’s important to research the keywords you intend to focus on. Don’t go for keywords that are too common, as they are very competitive and you are not likely to rank highly in search engines. Instead, try to pick less common keywords where possible, so the competition is not too fierce and you stand a fighting chance.

Inbound link

An inbound link is a link to your website from an external website. For example, if you run CoolWebsite.org and there is a page linking to this site from NeatForum.se, that is considered an inbound link; the link is coming in from an external website, to yours.


Keywords are words that are central to your content’s topic: they’re what you’re writing about. As far as SEO is concerned, keywords are the words and phrases people are typing into Google to find your content.

Keywords are central to SEO, and perhaps the single most important factor you should consider. It’s important to research the keywords you intend to focus on. Don’t go for keywords that are too common, as they are very competitive and you are not likely to rank highly in search engines. Instead, try to pick less common keywords where possible, so the competition is not too fierce and you stand a fighting chance.

If you run a website selling televisions, and you decide to focus on the keyword “TV”, you are likely to find the competition is far, far too great – your website is very unlikely to rank highly in Google, as hundreds and thousands of other pages already exist and are competing over the lucrative “TV” keyword.

Keyword density

Keyword density refers to the percentage of your content made up of your keyword. If you have a page containing 1,000 words, and 100 of those words are your keyword, you would have a 10% keyword density.

Keyword density is important to search engines; the higher the keyword density, the more relevant a website or web page is considered to be. However, there is a limit: if a page contains a very high keyword density, search engines like Google are likely to consider the page spammy.

While there is no agreed-upon percentage, and search engines don’t publish any exact figures, it is commonly said that a keyword density above 2-5% is likely to negatively affect a web page’s search ranking, as it will be considered keyword stuffing (see below).

There are a great many factors that search engines look at when deciding how to rank a web page, and keyword density is just one of those factors.

Keyword stuffing

As detailed above, keyword stuffing is the practice of filling a page with keywords, in an attempt to positively influence the page’s search ranking.

Modern search engines such as Google and Bing can accurately detect keyword stuffing, and are likely to penalise a site for engaging in this negative practice.


Latent Semantic Indexing (LSI) is a mathematical technique that attempts to find the relationship between words, to enable better understanding of information.

Despite LSI being a hot topic in SEO communities, there is actually very little evidence it plays a role in how search engines choose to rank sites.

Link building

Link building is the practice of increasing the amount of external links pointing to your website. It is very important to SEO: search engines consider sites with many inbound links to be more relevant than sites with fewer inbound links, and this will affect how the search engine ranks the website.

Done correctly, link building is the surest way to increase a website’s ranking. Done incorrectly, search engines may consider a website to be “spammy” and potentially penalise (rank down) a website and its pages.

The anchor text (the text you click on when following a link, for example “Wikipedia” in the following link: Wikipedia) is important in how relevant a search engine considers a page to be. For example, if hundreds of websites link to yours with the anchor text “Free TVs”, Google is likely to consider your page highly relevant for that keyword, and people searching “Free TVs” in Google will find your website.

Link farm

A link farm is a website created in order to link to other websites or pages, in an attempt to improve the website or page’s search ranking.

Link reputation

Also known as link authority, link reputation refers to how reputable and relevant a link is considered to be for its anchor text.

Link rot

Link rot is caused when links point to content that is permanently unavailable, often the result of content being moved around, renamed or removed, resulting in 404s, or because the link points to a website that has ceased to exist.

From an SEO perspective, link rot and dead links are a negative thing; it’s important to avoid dead links by frequently updating pages to ensure content linked is available and relevant.

Search engines will likely look negatively upon pages containing many dead links.

Meta keywords

These are the keywords used in the HTML <meta> tags of pages; they are used (among many other things) by search engines to determine the topic of a page’s content. Visitors to a page cannot see them, unless they inspect a page’s HTML source code.

For example, a page about football may contain meta keywords such as “football”, “soccer”, “footie”, “football purchase”, “football news”, and so on.

Once an important factor of successful SEO, meta keywords are no longer particularly useful. Search engines do not give meta keywords much weight, and many SEO agencies advise against their use, considering it unproductive or a waste of time better spent on other aspects of search engine optimisation.

Negative SEO

Negative SEO refers to any attempt to negatively impact another web page’s search ranking, for instance the ranking of a competitor.

This is often achieved by submitting links to the site on link farms, or other such pages, or by posting spam comments containing the website’s link: search engines will think the website is behaving in a spammy way, and may penalise it.


An optional value given to the rel attribute of an HTML link, nofollow tells search engines the link should not influence the ranking of the website or page it points to.

Outbound link

An outbound link is a link from your website to an external website. For example, if you run CoolWebsite.org and link to NeatForum.se, that’s an outbound link. The link is going out of your website to some external site.


In advertising, the Pay-Per-Click (PPC) model is one in which an advertiser pays the publisher when an advertisement is clicked.


PageRank is one of the many algorithms used by Google to determine how a web page should rank.


Search engines may levy a penalty on a website engaging in unethical, negative SEO practices, such as spamming or performing Negative SEO on its competitors.

Poisonous word

Sometimes called a poison word or death word, poisonous words are words commonly associated with spam content. For example, “Viagra” may be considered a poisonous word in certain contexts, due to its frequency in email spam campaigns.


Another ranking algorithm used by Google, Query Deserves Freshness (QDF) is used by Google to try to identify user’s searching for new, “fresh” content.


Return on Investment (ROI) is a performance measure, commonly used to measure the efficiency of an advertising or SEO campaign. It is the net profit divided by the cost of the investment, then multiplied by 100.


Rich Site Summary (RSS; alternatively Really Simple Syndication) is a sort of web feed. Users subscribe to an RSS feed to receive updates to web content. News sites and blogs commonly use RSS, though RSS plays a diminished role on the modern Web compared to 10 years ago.


A text file stored on a server, used to instruct search engine crawlers’ (and other general crawlers, or ‘bots’) on pages, directories and content which should not be visited. Read more here: http://www.robotstxt.org/robotstxt.html


A closely related term to SEO, SEM stands for Search Engine Marketing, and essentially refers to a website improving the ranking of its pages via paid advertising.


Search Engine Optimisation (also spelt Optimization) refers to the best practices, methods and techniques to improve how a website or page ranks in search engines.

Site Map

A site map is a map of the pages of a website.


Some call it a spider, others a bot, some a crawler, but they all refer to the same thing: the software used by search engines to visit, or “crawl”, your website, and explore the links found within. See also robots.txt above.


URLs (Uniform Resource Locators) are the “links” used in the modern Web, e.g. https://en.wikipedia.org, or https://reddit.com, and so on.


Virtual Private Networks (VPNs) are a way of tunnelling your data through another server, hiding your IP behind the IP of the server. While VPNs are useful for staying anonymous online and preventing snooping from your employer, school or ISP, they are also useful from an SEO perspective; for instance, using a German VPN server, you could perform local SEO research as Google will give you localised results. To learn more about VPNs, read What is a VPN? or explore this glossary of VPN terminology.


A system used to look up information about a website or IP address.


Extensible Markup Language (XML) is a markup language, similar to HTML, used to define a set of rules for encoding documents. XML is designed to be “human-readable”, and you can read more about XML on the W3C’s website: https://www.w3.org/XML/