The short three letter term lag refers specifically to the project management technique that refers to the logical relationship that exists for the primary purpose of causing or providing the resulting variable of a noteworthy or significant delay in the initiation of the following and succeeding activities and work schedule events to take place. One particular example of the term lag would be an example such as that of the finish-to-start dependency in an instance in which a 10 day lag exists, the next activity, referred to as the successor activity, cannot be initiated under any circumstances unless and until the 10 full days have passed by from the point at which the preceding activity has come to conclusion and or a resolution. Lag is sometimes inserted into the scheduling of an activity in cases in which the project work components require overlapping personnel requirements and there is a need to build in a delay to assure that the succeeding activity is properly manned and properly staffed.
This term is defined in the 3rd and the 4th edition of the PMBOK.