RISC-5 is a CPU architecture like x86 (AMD and Intel) or ARM (Qualcomm, Apple, Samsung, Google).
It's main differences are that it is an open architecture. It is still early in it's life cycle but it's already showing promising advancement.
I'm not as well educated on this part of it but I remember reading that it is more efficient for a certain types of common calculations that have long since been an issue for x86. As noted though citation needed.