Editing : Edit Modes and Tools : Slip Mode

Slip Mode
In Slip mode, clips can be moved freely within a track or to other tracks. In this mode, it is possible to place a clip so that there is space between it and other clips in a track. When the track is played back, this space is silent. It is also possible to move a clip so that it overlaps or completely covers another clip.
Use Slip mode when you want the Trim, Selector, Grabber, and Pencil tools to work without any restrictions to placement in time.