What context are we speaking in? I assume you're talking about radio equipment... in that case a "module" is probably referring to the antenna unit that attaches to the transmitter and sends out the signal to the receiver (and in some cases receives telemetry information back). No, any radio I've seen - especially 2.4GHz - comes with a module with/in the transmitter. Most of the time they sell them as replacements in case it breaks, then you don't have to buy a whole new transmitter.