RTF (which stands for Rich Text Format) is a document formatting language that uses simple commands to specify the formatting of a document. These commands, or tags, as they are called, are ASCII strings, like \par (the tag that marks the beginning of a new paragraph) or \b (the tag that turns on the bold style). 

RTF docuemnts don't contain special characters and can be exchanged among different operating systems and computers, as long as there is an RTF capable application to read the document.