Not sure it necessarily stands for anything, maybe it's just a code FCA uses for that body style. Although I could be wrong. Kinda like the E-body was the Barracuda/Cuda and Challenger in the early 70s. I could ask some of the engineers at work, they make the seats for the Cherokee, among things. (Sadly not the Compass though. Lol)
Chassis code. MK was the 1st Gen compass, MP is the new compass (US market), ML, MM, MN are in other markets (Brazil, India, China..etc)
The 95-99 neon was PL, 00-05 was PL2, PT cruiser is PT, renegade is BU it goes on and on.