1. The name of the commodity. - Amplifier
2. The number of them in the "Stack".
2 channels
3. Why they are a "Short Stack". Because the "tall stack" is the current, 5 channel Outlaw 750 amp - so a 2 channel amp would be a "short stack". In order to support a 7.1 pre/pro you need the 2 channel short stack and the 5 channel 750/tall stack.