An In-Memory Data Structure Store is a type of database that stores data directly in the main memory (RAM) of a computer, rather than on traditional disk storage. This allows for much faster data access and processing speeds, making it ideal for applications that require real-time data retrieval and manipulation. Common examples include systems used for caching, session management, and high-performance computing. These stores often use data structures like hash tables, lists, and trees to organize and manage data efficiently. Popular implementations include technologies like Redis and Memcached, which are widely used in web applications to enhance performance by reducing latency in data access.