WordNet (r) 3.0 (2006):

reduced instruction set computer
    n 1: (computer science) a kind of computer architecture that has
         a relatively small set of computer instructions that it can
         perform [syn: reduced instruction set computing, reduced
         instruction set computer, RISC] [ant: CISC, complex
         instruction set computer, complex instruction set
         computing]

The Free On-line Dictionary of Computing (30 December 2018):

Reduced Instruction Set Computer
RISC

    (RISC) A processor whose design is based on the
   rapid execution of a sequence of simple instructions rather
   than on the provision of a large variety of complex
   instructions (as in a Complex Instruction Set Computer).

   Features which are generally found in RISC designs are uniform
   instruction encoding (e.g. the op-code is always in the same
   bit positions in each instruction which is always one word
   long), which allows faster decoding; a homogenous register
   set, allowing any register to be used in any context and
   simplifying compiler design; and simple addressing modes
   with more complex modes replaced by sequences of simple
   arithmetic instructions.

   Examples of (more or less) RISC processors are the Berkeley
   RISC, HP-PA, Clipper, i960, AMD 29000, MIPS R2000
   and DEC Alpha.  IBM's first RISC computer was the RT/PC
   (IBM 801), they now produce the RISC-based RISC
   System/6000 and SP/2 lines.

   Despite Apple Computer's bogus claims for their
   PowerPC-based Macintoshes, the first RISC processor used
   in a personal computer was the Advanced RISC Machine (ARM)
   used in the Acorn Archimedes.

   (1997-06-03)