Task 2 cannot finish until the start of Task 1 – they have a Start-to-Finish dependency.
When the start date of Task 1 determines the finish date of Task 2, the tasks have a Start-to-Finish (SF) dependency.
In Project this is how you create just-in-time scheduling. For example, if a related task needs to finish before a milestone or project finish date, but it doesn't matter exactly when and you don't want a late finish to affect the just-in-time task, you can create an SF dependency between the task you want scheduled just in time (the predecessor) and its related task (the successor).
In the real world the SF dependency type occurs less frequently than the other types of dependencies.