Microsoft Compiled HTML Help is a Microsoft proprietary online help format. It was introduced as the successor to Microsoft WinHelp with the release of Windows 98 and is still supported in Windows 7.
HyperText Markup Language (HTML) is the main markup language for web pages. HTML elements are the basic building-blocks of webpages.
HTML is written in the form of HTML elements consisting of tags enclosed in angle brackets (like <html>), within the web page content. HTML tags most commonly come in pairs like <h1> and </h1>, although some tags, known as empty elements, are unpaired, for example <img>. The first tag in a pair is the start tag, the second tag is the end tag (they are also called opening tags and closing tags). In between these tags web designers can add text, tags, comments and other types of text-based content.
Portable Document Format (PDF) is a file format used to represent documents in a manner independent of application software, hardware, and operating systems. Each PDF file encapsulates a complete description of a fixed-layout flat document, including the text, fonts, graphics, and other information needed to display it. In 1991, Adobe Systems co-founder John Warnock outlined a system called "Camelot" that evolved into PDF.
The Rich Text Format (often abbreviated RTF) is a proprietary document file format with published specification developed by Microsoft Corporation since 1987 for Microsoft products and for cross-platform document interchange.
Most word processors are able to read and write some versions of RTF. There are several different revisions of RTF specification and portability of files will depend on what version of RTF is being used. RTF specifications are changed and published with major Microsoft Word and Office versions.
Web help is a type of online help that can either be delivered through the internet or as a stand-alone set of HTML files on a computer. A well-known example of such a system is WebHelp.Com. This approach, mixing internet and local resources, is also used in Windows XP's Help and Support feature.