In relation to project activities, slack or slack time means that there is more time available to complete an activity than needed. Activities with slack are not on the critical path.
calculated time span during which an event has to occur within the logical and imposed constraints of the network, without affecting the total project duration. Note 1: it may be made negative by an imposed date. Note 2. the term slack is used as referring only to an event.
Refers to spare time. This extra time can be calculated for the critical path by taking Deadline less the Input Arrival less the sum of Operation Durations.