Hypertext is a kind of specially-formatted text that provides a link to other content. Hypertext allows system designers to organize information in a branching structure instead of a linear one. Clicking a hypertext link (called a hyperlink) will send the user to another part of the current document or a separate document entirely. Hypertext links are a fundamental building block of the Internet, allowing users to navigate in a web browser from page to page and from site to site.
The use of hypertext predates the Internet, dating back to the 1960s. It allows documents in a system to cross-reference each other and provide quick access to information. Dictionary and encyclopedia software use hypertext to link from one article or definition to another. Apple's HyperCard software used hypertext (as well as hyperlinks added to images) to allow users to create and navigate a flat-file database, which people used to create everything from simple databases to presentations to interactive choose-your-own-adventure games.
Hypertext served as the basis for the original information-sharing system that became the World Wide Web, and its usefulness helped spur the growth of the web on the Internet. Hypertext is used on virtually every single web page on every single website. Hypertext links are also still used in many types of documents, helping users navigate long text documents and spreadsheets.
NOTE: Similarly-formatted images and videos that provide links to other content are commonly called "hypermedia."