Definition: A click track is, basically, a metronome designed to give the artists recording a reference for tempo. A click track can be inserted via plug-ins in most audio programs, or can be done externally via MIDI or a metronome.
Having every musician in on the same tempo reference -- especially the drummer -- will make overdubs much easier!
Also Known As: Metronome, reference track.
"It's not up for debate: your drummer WILL use a click track so that everyone else is on the right beat."