Verb. To synchronise two or more iPods to the same album/playlist. This is often done on a bus or at school so those who are sync'd all hear the same music at the exact same time, as if it was being played on a loudspeaker nearby.
This can either be used to make a silent synchronised dance party that confuses the hell out of all non-sync'd people in the immediate vicinity, or allows those involved in the sync to enjoy songs simultaneously, without the need for big audio equipment or the disturbance of others.
Perfect timing for starting respective albums/playlists is essential and requires much practice.
Lucas: God, this bus trip is taking forever! Wanna sync?
Jim: Sure, how about we sync that legit playlist I made last week?