When he didn't get the pay raise he was expecting, he had to take another job to 'pick up the slack'. [=to make up for the money he was not making]
The manager has to 'take up the slack' when employees don't do their jobs correctly.
We left some 'slack' in the budget so that we can hire more people if we have to.
(..) I mean, it blows my mind. We're hung up on this notion we have some... ...obligation to help the struggling black man. Cut him some slack until he can overcome these historical injustices. It's crap. This stuff you guys are saying perpetuates it. All this liberal nonsense. (..)1998 American History X