The terms leads and lags are used to identify and control the timing of various activities within the project. It is important to accurately document leads and lags.
Lead Time: Let's assume a project has two pieces that need to be completed at the same time. Work package A will take 4 weeks to complete, but work package B only takes one week. B would show in the project plan as a finish to start (FS) with a one week lead. This means the B work package component should start one week before A is scheduled to be completed.
Lag Time : Lag time can best be described as a planned or forced delay. A great example of this is a construction project that involves pouring concrete. The project plan must include a lag time of 2 days for the concrete to dry before the next phase can begin.
Hammock Activity: Hammock activity is also frequently referred to as summary activity. These are activities that are roughly related and are reported as a single activity. Some times the relationship between the activities is clear, other times they may only be related because their completion leads to the same result. On a gantt chart a hammock activity is usually displayed as a thick black bar above a grouping of lower level activities.
Cornelius Fichtner, PMP