SQLite is an relational database management system contained in a relatively small C library. SQLite is a public domain project developed by D. Richard Hipp.
The SQLite is not a standard relational database management system, but is part of the program that uses it. The primary communication between SQLite and the host program is done via API calls within the programming language. This lessens the database communication overhead and simplifies the development. The database is stored as a single standard file on the host machine.
The SQLite database implements most of SQL-92 standard, including transactions (ACID), triggers and most of complex nested queries. One of the drawbacks of SQLite is the lack of type checking.
SQLite is multi-process database (more than one process can access the same database). Several read accesses processes can run simultaneously, but only one process can write to the database in any given moment.
You can query SQLite database through a program called SQLite.