X9, overdriving an amp, makes a distorted sound. If this is a question about effects pedals, Brand A Distortion Pedal vs Brand B Overdrive Pedal, it's basically the same thing, just manufacturers choose different words,ie... King Elwood's Mega-Metal Ultimate Shred Distortion Pedal or Mr. Melvin's Death Ray Killer Laser Beam Overdrive Machine, just a marketing ploy!