Asymmetric multiprocessing, or AMP, was a software stopgap for handling multiple CPUs before symmetric multiprocessing, or SMP, was available.
Multiprocessing is the use of more than one CPU in a computer system. The CPU is the arithmetic and logic engine that executes user applications; an I/O interface such as a GPU, even if it is implemented using an embedded processor, does not constitute a CPU because it does not run the user's application program. With multiple CPUs, more than one set of program instructions can be executed at the same time. All of the CPUs have the same user-mode instruction set, so a running job can be rescheduled from one CPU to another.
Read more about Asymmetric Multiprocessing: Background and History, Burroughs B5000, IBM System/360 Models 65MP and 67-2, CDC 6500 and 6700, DECsystem-1055, Univac 1108-II, Multics, IBM System/370 Model 168