A CAPTCHA is field in a web form, designed to differentiate between users and bots. Typically a CAPTCHA consist of an image containing letters that are difficult to read. The user must then enter those letters into a text box on the form. The goal is to reduce form spam by making the letters unreadable to bots, but readable to humans.
Case-sensitive systems differentiate between uppercase and lowercase. "ABC" and "abc" are not the same thing on a case sensitive system. In web design it's important to note that hosting servers running MS Windows are not case-sensitive (contactus.htm and ContactUs.htm are treated as the same file) while servers running Linux are case-sensitive (if the file is saved as contactus.htm, a link to ContactUs.htm would produce an error.) This is something to watch out for when changing from one operating system to another.
Cloaking is a technique where the web site serves different content to different users, based on their IP. While there are legitimate uses for cloaking (such as delivering different content for users from different countries), the technique is not recommended. Cloaking can be used to serve the real site to human visitors and different (optimized) content to search engine spiders. When detected, a cloaked site is usually penalized and may be even be banned from the search results.
In web design terms, a cluttered page is a page where the design elements (navigation, images, text) are bunched together so tightly that the user has trouble finding what they came looking for.
Clutter can also refer to the content. If the entire page is focused on selling a hairbrush and there is a link to a site that sells bottled water, that link can be considered clutter. It distracts from the purpose of the page.
A content management system (CMS) offers a way for a user to edit the content of a web site from within a browser-based interface, without any HTML skills required. This is a feature often built into a web site by the developer, allowing the web site owner to add, remove or change the content themselves.
In the context of web design, conversion rate (CR) refers to the percentage of web site visitors that take the intended action such as signing up for a newsletter or making a purchase. In other words, what percentage of your web site visitors do what you want them to do.
This is an extremely important factor in measuring the success of a web site. Ideally every element of the web design, such as choice of colors and navigation architecture, should aim to increase the web site CR.
In web design, a cookie is a small text file that a web site saves on a user's computer. The cookie stores information about that user. On the user's next visit to the same web site, the web site retrieves the cookie to access the information. Cookies are useful for saving bits of information like user preferences.
CSS (Cascading Style Sheet) is a style sheet language that determines the look of elements on a web page. Web sites can be built without CSS (it came many years after HTML), but CSS gives the web designer more power to control how the content is displayed. The main benefit of CSS is that it splits the content from the presentation. Site-wide style changes can be performed by editing the style sheet rather than every page individually.