what is slack in project management

Free slack:

The free slack of an activity is the time this activity can be delayed without impact on the following activity.

Total slack:

The total slack of an activity is the time this activity can be delayed without impact on the finish date of the project.

The Least Slack Time scheduling algorithm is used for assigning priority based on the slack time (temporal difference between the deadline, ready time and run time) of a process.

Slack means different things, depending on context. For this question, I assume that slack is the time that somebody is waiting for somebody else to do something.

Slack simulation, then, is a simulation where you evaluate different efficiencies and/or worker/consumer ratios, in an attempt to minimize or optimize slack, i.e. wasted, time.

Slack or Float is the amount of time an activity can get delayed without delaying the overall end date of a project