overdub?

i heard that many of heavy metal band use overdub. what kind of effect is that (i guess it's effect)... is it maybe something like reverb?

Overdub is a recording term. It means recording a song piece by piece. Usually first you do the drums then bass and then rythm guitar and down the line. It's a prefered technique rather than recording the band all at once. Why? Well say The whole band is doing a take and everyone does a good take but the bassist misses a note or something. Everyone has to do the take over. Something to that effect.