Click-Through - The action of clicking on a link to visit a web page.
Click-Through-Rate (CTR) - The number of times a link is clicked on divided by the number of times that same link is displayed (called an impression).
Example: A link is displayed 100 times (100 impressions) and clicked on 5 times. The CTR is 5% (5/100=.05).
Call-to-action link - Otherwise known as a hyperlink. Call-to-action links in Internet marketing campaigns guide the reader to a new action step. Call-to-action hyperlinks could lead a prospect to a new Web page, an email form, a text section within a page or a shopping cart. Correctly written, call-to-action links increase micro-conversion rates and can affect keyphrase relevancy.
Cloaking - Serving one version of a page to a human visitor and a different version of the same page to the search engines. This is usually done to "fool" the search engines into giving the page a higher rank than it would normally receive while making sure the human visitor sees a useful and attractive page.
Note: Cloaking is discouraged by most major search engines, including Google.
Comment Tags - Used in a web page's HTML source code to indicate certain information about a section of the page code. Some search engines will consider keywords contained in comment tags for keyword density purposes, others (including Google) will not.
Example:
<!--This is a comment-->
Content - The information located on a web page. This includes text, images, and any other types of information that a webmaster places on the page.
Conversion rates - Conversion rates are distinct measurements that determine how many of your prospects take your preferred action step. Typically, micro-conversions (for instance, reading different pages on your site, or signing up for a newsletter) lead to your main conversion step (making a purchase, or contacting you for more information).
Counter - A script that counts the number of hits, unique visitors, and/or page views that a web page (or an entire site) receives. These "stats" provide very useful information for the webmaster.
Crawler - A program used by search engines to "crawl" the web by following links from page to page. This is how most search engines "find" the web pages that they place in their index. Also referred to as a spider or robot.
Crawling The Web - Search engines use crawlers to move from web page to web page by following the links on the pages. The pages "found" are then ranked using an algorithm and indexed into the search engine database.
Cross Linking - This is where the owner of two or more websites interlink the sites in order to boost their search engine rankings. If detected, cross linking often results in a search engine penalty.
Cascading Style Sheets (CSS) - Cascading Style Sheets (CSS) is a simple mechanism for adding style (e.g. fonts, colors and spacing) to Web pages. CSS is a standard layout language for the Web, one that controls colors, typography, and the size and placement of elements and images. CSS is intended by its creators, World Wide Web Consortium (W3C) to replace HTML table based layouts, frames, and other presentational hacks. CSS, together with other web standards such as XHTML, helps us separate style from content, making the Web more accessible, and opening it up to more powerful applications and technologies to come.