A memory cache is a small, high-speed storage area located within a computer's main memory. It temporarily holds frequently accessed data and instructions, allowing the processor to retrieve them quickly without needing to access slower storage options like hard drives. This speeds up overall system performance and enhances user experience. Caches can be found in various forms, such as CPU caches (like L1, L2, and L3) and web caches that store copies of web pages. By reducing the time it takes to access data, memory caches play a crucial role in optimizing the efficiency of computing systems and applications.