Clips can be launched by assigning notes to the clip. For more info see here
Toggle: Acts like a switch upon receiving a note.
Gate : Clip stays active as long as a note is received. In other words, a clip becomes active on Note_On and inactive on Note_Off.
Trigger : A clip becomes active on Note_On and deactivates itself after running once.
Arp! : Like Gate, except that the clips are not triggered by the assigned note, but by every note.
Let's say you have three clips with Launch=Arp! and you play a three note chord. The first clip reacts on the lowest note, the second on the middle one, and the third on the highest note.
The midi-channel used to launch a clip in Arp! mode is the same as the channel used to Transpose clips.