Memcached is an open-source, high-performance, distributed memory caching system designed to speed up dynamic web applications by alleviating database load. It operates by storing data and objects in RAM, reducing the time taken to access these frequently requested pieces of data. Widely used in large-scale system architectures, Memcached enhances scalability by managing short-term data storage needs efficiently. With its simple and easy-to-use design, Memcached helps developers optimize web application performance.