A Memory Management Unit (MMU) is a hardware component in a computer that manages the memory and addresses used by the system. It translates virtual addresses generated by the CPU into physical addresses in the computer's memory. This allows programs to use memory more efficiently and securely, as each program operates in its own virtual address space. The MMU also handles memory protection and allocation, ensuring that one program cannot access the memory space of another. This is crucial for system stability and security, as it prevents unauthorized access and potential crashes. Overall, the MMU plays a vital role in modern computing systems.