pick up the slack

Short definition from Wiktionary

Verb

1. 1
   Alternative form of take up the slack: To tighten something that is slack so that it is taut.
2. 2
   Alternative form of take up the slack: To do work that would otherwise be left undone.
3. 3
   Alternative form of take up the slack: To provide extra needed resources.
4. 4
   Alternative form of take up the slack: To act as a slack variable, converting an inequality into an equality.
5. 5
   Alternative form of take up the slack: To consume something that would otherwise go to waste.