What is the difference between the lage and Lead at time management in construction projects?

Lag and Lead_

Lag : The amount of time the successor activity can be delayed with respect to a predecessor activity is Lag.

Lead : The amount of time the successor activity can be advanced with respect to a predecessor activity is lead.

A lead is the amount of time whereby a successor activity can be advanced with respect to a predecessor activity. So in this case the second task can start N days before the end date of the first task.A lag is the amount of time whereby a successor activity will be delayed with respect to a predecessor activity. In this case the second task can start only N days after the end date of the first task.

Lag

The amount of time whereby a successor activity will be delayed with respect to a predecessor activity.

For example: When building two walls from a novel design, one might start the second wall 2 days after the first so that the second team can learn from the first. This is an example of a lag in a Start-Start relationship.

Lead

The amount of time whereby a successor activity can be advanced with respect to a predecessor activity.

For example, on a project to construct a new office building, the landscaping could be scheduled to start prior to the scheduled punch list completion.