An In-Memory Database (IMDB) is a type of database that stores data directly in the main memory (RAM) rather than on traditional disk storage. This allows for much faster data retrieval and processing, making it ideal for applications that require real-time analytics and quick response times. IMDBs are often used in scenarios like online transaction processing and big data analytics. Because data is stored in memory, IMDBs can be more volatile than disk-based databases, meaning that data can be lost if the system crashes or loses power. However, many IMDBs offer features like data persistence and backup options to mitigate this risk. Popular examples of IMDBs include Redis and Memcached.