TL;DR
Also called: too long; didn't read
The abbreviation tl;dr stands for too long, didn't read.
It is used to indicate that a text is too long and therefore not interesting to read. Besides an excuse for not reading, responding with tl;dr is an indictment to the writer that the text is too long, woolly and not to the point.
Also, tl;dr is sometimes used as an announcement preceding a summary of a long text. The term is used in online discussion forums, among other places.