Cost Per Click (CPC) Advertising: Service provided by Search Engines. Advertisers bid on keywords relevant to their business. The search results are delivered in the order of highest to lowest bid. Advertisers are charged the bid amount when a user clicks through.

Directory: A server or a collection of servers dedicated to indexing Internet web pages and returning lists of pages, which match particular queries. Directories (also known as Indexes) are normally compiled manually, by user submission, and often involve an editorial selection and/or categorization process (such as Yahoo)

Domain: A sub-set of Internet addresses. Domains are hierarchical, and lower-level domains often refer to particular web sites within a top-level domain. The most significant part of the address comes at the end - typical top-level domains are .com, .edu, .gov, .org (which sub-divide addresses into areas of use). There are also various geographic top-level domains (e.g. .co.uk .ca, .fr, etc.) referring to particular countries.

Dynamic content: Information on web pages, which changes or is changed automatically, e.g. based on database content or user information. Sometimes it's possible to spot that this technique is being used, e.g. if the URL ends with .asp, .cfm, .cgi or .shtml. It is possible to serve dynamic content using standard (normally static) .htm or .html type pages, though. Search Engines will currently index dynamic content in a similar fashion to static content, although they will not usually index URLs which contain the ? character.

Heading: Many Search Engines give extra weight and importance to the text found inside HTML heading sections (e.g. H1 tags). It is generally considered good advice to use headings when designing web pages and to place keywords inside headings.

HTML Emails: Email sent in Hyper Text Markup Language – usually to improve impact/appearance of email message.

Keyword: A word, which forms (part of) a Search Engine query.

Meta tag: A construct placed in the HTML header of a web page, providing information, which is not visible to browsers. The most common meta tags (and those most relevant to Search Engines) are KEYWORDS and DESCRIPTION. The KEYWORDS tag allows the author to emphasise the importance of certain words and phrases used within the page. Some Search Engines will respond to this information - others will ignore it.

Optimisation: Changes made to a web page to improve the positioning of that page with one or more Search Engines. A means of helping potential customers or visitors to find a web site. Optimisation may involve design/layout changes, new text for the title-tags, meta-tags, alt- attributes, headings, and changes to the first 200-250 words of the main text. A large image map at the top of a page should be moved further down the page. Frames should be avoided (unless navigational links are also provided within the frames).

Relevancy: How well a document provides the information a user is looking for, as measured by the user.

Search Engine: The software that searches an index and returns matches. Search engine is often used synonymously with spider and index, although these are separate components that work with the engine.

Spider: The software that scans documents and adds them to an index by following links. Spider is often used as a synonym for Search Engine.