- (Internet) too long; didn't read. Used to indicate that one didn't read the whole text.
- (Internet) too long; didn't read. Used to indicate that what follows is a summary of the overly long text.
An example of TLDR is a comment in an email to respond to a long dissertation by another person.
tldr - Computer Definition
(Too Long Didn't Read) Internet slang for a summary that appears at the beginning of an article or that describes a lengthy article that the person did not bother to fully read. TL;DR (with a semicolon) is a variant. BLUF (Bottom Line Up Front) is another term for a preceding summary. See digispeak.