Playback and Recording : Record Setup : Record Modes : QuickPunch

QuickPunch
QuickPunch gives you the ability to manually and instantaneously punch in (initiate recording) and punch out (stop recording) on record-enabled audio tracks during playback by clicking the Record button in the Transport. Recording with QuickPunch is nondestructive.
When using QuickPunch, Pro Tools begins recording a new file when playback begins, automatically generating clips in that file at each punch in/out point. These clips appear in the track’s playlist; and the complete audio file appears in the Clip List along with the QuickPunch created clips. Up to 200 of these “running punches” can be performed in a single pass.
Though you can punch record in the other record modes by manually specifying the record range, only QuickPunch provides instantaneous monitor switching on punch-out.