'Word clock' is used to synchronize digital audio, and is built in to S/PDIF (which the MPC uses). Digital audio is divided into blocks and whatever recieves those blocks has to know when one ends and the other starts, otherwise there will be clicks in the audio. The MPC automatically syncs up to an external device.
MTC is used to synchronize the MPC with a DAW (computer software) for example, and is found under 'midi/other' I would guess.