Instruction Set Architecture (ISA) is a critical component of computer architecture that defines the set of instructions a processor can execute. It serves as the interface between software and hardware, specifying how programs communicate with the CPU. The ISA includes details about the data types, registers, addressing modes, and the operations that can be performed. Different types of ISAs exist, such as RISC (Reduced Instruction Set Computer) and CISC (Complex Instruction Set Computer). RISC focuses on a small set of simple instructions for efficiency, while CISC includes a larger set of more complex instructions. Understanding ISA is essential for software developers and hardware engineers alike.