Instruction Set Extensions are additional instructions added to a computer's basic instruction set architecture (ISA) to enhance its capabilities. These extensions allow processors to perform specific tasks more efficiently, such as multimedia processing or cryptographic operations. By incorporating these specialized instructions, developers can optimize software performance and improve overall system efficiency. Common examples of instruction set extensions include SSE and AVX for multimedia processing, and AES-NI for encryption. These extensions are designed to work alongside the existing instructions, enabling programmers to leverage advanced features without needing to redesign the entire processor architecture.