SQLite is a self-contained, serverless, zero-configuration, transactional SQL database engine. It is embedded into the end program. Unlike client/server database management systems, the SQLite engine operates directly on ordinary disk files. A complete SQL database with multiple tables, indices, triggers, and views, is contained in a single disk file. The file format is cross-platform, meaning a database created on one architecture can be read on another. SQLite is widely used as an embedded database for local/client storage in application software such as web browsers. It's also a popular choice for small to medium-sized websites and embedded devices. SQLite databases are often used for storing application settings, user data, and other persistent information. The 'sqlite3' file extension is commonly used to denote these database files, although other extensions like '.db' or '.sqlite' are also frequently encountered.