In the context of project management, the term “free float” is used to describe amount of time that spans from the completion of one previously scheduled activity and extends to the point at which the next scheduled activity is set to begin. Free float can be calculated by determining the amount of the time between the earliest start date of the initial activity and the earliest start date of the succeeding activity, and then subtracting from that total the amount of time that it is expected the first activity will take to complete. During this period of free float, the completion time or date of the earlier of the activities can be extended up until the scheduled early start date or time of the next scheduled activity without causing delays. If there is no succeeding activity scheduled, the project end date would be used to determine the back end of the free float window.
This term is defined in the 3rd and the 4th edition of the PMBOK.