Let's see if we can unconfuse you. To oversimplify, bi-amping means powering two separate speakers in the same cabinet with two separate amplifiers - one handling the low frequencies, the other the mids and highs. (Of course it also can be used for lots of separate speakers in different cabs, but you get the idea.) It can be used in a whole range of applications, in particular home stereo, bass guitar amplification, PA and, as you say, monitors.
Most active monitors are bi-amped - that is to say, each box has two separate amps. So a pair has four amps. When the signal hits the monitor, it goes through a crossover, which splits out the lows and sends them to the woofer amp. You can also do this with bi-ampable passive speakers (like most mid to high market hi-fi kit these days) by using an external crossover and two separate amplifiers.
It has nothing to do with using an amp in one speaker cabinet to also power another cab (which is what most multimedia active systems do). Hope that helps.
