Slack

Slack is the amount of time in a task plan where a task can be delayed without causing another task (or the task plan itself) to be delayed. Slack is also referred to as float. There are two types of slack: free slack and total slack. Free slack is the amount of time that a single task can be delayed before that delay causes another task in the task plan (or the task plan itself) to be delayed. Total slack is the amount of time that one or more tasks in a task plan can be delayed before that delay causes the task plan to be delayed.