Instruction set refers to the Assembly syntax based on a processor's architecture that interacts with its registers within the processing unit itself. There is a large variety of instruction sets including: MIPS, ARM, 68HC11/12, x86, and so forth.
The instruction set, also called instruction set architecture (ISA), is part of a computer that pertains to programming, which is basically machine language. The instruction set provides commands to the processor, to tell it what it needs to do. The instruction set consists of addressing modes, instructions, native data types, registers, memory architecture, interrupt, and exception handling, and external I/O.