Machine instructions are the basic commands that a computer's central processing unit (CPU) understands and executes. These instructions are written in a low-level programming language called machine language, which consists of binary code (0s and 1s). Each instruction tells the CPU to perform specific tasks, such as adding numbers, moving data, or controlling input and output devices. Machine instructions are crucial for the operation of software applications and the overall functioning of a computer. They form the foundation of higher-level programming languages, like Python or Java, which are more user-friendly but ultimately get translated into machine instructions for the CPU to execute.