Discrete MultiTone Modulation
Discrete MultiTone Modulation is a modulation method where the available bandwidth is divided into a large number of channels. Data is allocated to maximize the throughput of every channel. Channels that can't carry data are not used, and the bandwidth reallocated.
DMT is the technology which divides the whole bandwidth on the telephone line into lots of sub-channels and then controlling these 'virtual modems' as one together in order to get higher speeds.