Glossary: Lead Time
Lead time is a duration you can put on a dependency to mean that some amount of time is needed between the two moments involved. For example, a Start→Start dependency with a lead time of 1 day means that after the first task starts, the second task can start one day later.
Lead time can be negative; for instance a Finish→Start dependency with a -2 hour lead time will allow the second task to start once the first task is 2 hours from completion.
You can set up lead time by typing a duration (such as +3w or -2d4h) either a the end of a dependency code in the Dependencies column of the task outline, or in the Task Dependencies inspector.
Lead time can also be a percentage of the predecessor task's duration; for example you could enter 100% for a lead time just as long as the task it comes after.