Random Question, and a Giggle.

I've seen tl;dr as a caption on LOLcat pics, and, just now, in a subject line in ionlylurkhere's journal. So as not to interupt any conversations among people who already get it --

What does it mean? Does the tl at least mean "talk later"?

Signed:
losing a bit of her geek!cred

Oh, and speaking of lolcats -- go here. It gave me the strongest giggle I've had in a while...