'Slack' is an acronym

Slack, the workplace productivity chat tool that lets you quietly discuss the merits of strawberry / frosted vs. brown-sugar / unfrosted PopTarts with a colleague for up to six hours at a time without anyone else noticing that you're being totally useless, is an acronym. The letters S-L-A-C-K stand for things.
But what?
Here are some of our guesses:Sorry Losers, America Chose KaitlynSo Long and Cool KeysStart Looking at Clark KentwhydoeshelookjustlikeSupermanbutwithglassesStop Licking: All