I want to know the meaning

These are not printing terma but types of document. PDF is a type of document (.pdf) that you cannot edit you can only see; you can open it with Adobe Reader HTML (.htm, .html) is practically like a web page (the vast majority of web pages are written in html); the formatting of the data inside is made by HTML tags; you can see the unformatted content with Notepad (for example) and the formatted one with any web browser RTF (.rtf, comes from rich text format) is a document that can accept formatting, such as bold, italic etc and it is usually seen and/or edited with MS Word XML (.XML) is a way of storing data in a file, also organized by tags; you can open it for example with Notepad I've no idea what postcript delimited is :)