The definition of TLDR is as an abbreviation for the phrase "too long, didn't read" or "too long, don't read", meaning the content of something is too boring or long to read.
An example of TLDR is a comment in an email to respond to a long dissertation by another person.
(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.
(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.