Switching a track (Or arming a track) means to convert it from input track to output track or vice versa.
Note: When the sequencer is not running, you can switch audio and midi tracks. When the sequencer is running, you can only switch audio tracks. Switching midi tracks from Play to Record will still play them (although recording will work), and switching midi tracks from Record to Play will not play them, as the midi information for the playing tracks is loaded before the sequencer starts.
When you switch a track from input to output, TP does the following:
The track continues from its current position, so you can have a track playing for example, then switch it to record at a position to start recording at that point.
Other types of tracks except midi and audio cannot be switched at run time.