In-Memory Databases are a type of database management system that stores data directly in the main memory (RAM) rather than on traditional disk storage. This allows for much faster data retrieval and processing speeds, making them ideal for applications that require real-time data access, such as online transaction processing and analytics. These databases often use data structures optimized for speed, enabling quick read and write operations. Popular examples of In-Memory Databases include Redis and SAP HANA, which are widely used in various industries to enhance performance and improve user experience.