Rich text is used to describe text data that is styled with fonts and formatting. As opposed to plain text, rich text allows the customization over character's size, color, font, formatting and more. Rich text is commonly used in word processors like Word and Google Docs.
Editors for rich text are commonly referred to as "WYSIWYG", or "What You See Is What You Get", because they display a stylized version of each character. In order to edit character and paragraph styles, they provide secondary interfaces, like inspectors or toolbars.
This is an example of Rich Text