What is SQLite ?

SQLite is a mostly ACID-compliant relational database management
system contained in a relatively small (~500kB) C programming library.

Unlike client-server database management systems, the SQLite engine is
not a standalone process with which the program communicates. Instead,
the SQLite library is linked in and thus becomes an integral part of
the program. The program uses SQLite's functionality through simple
function calls, which reduces latency in database access as function
calls are more efficient than inter-process communication. The entire
database (definitions, tables, indices, and the data itself) is stored
as a single cross-platform file on a host machine. This simple design
is achieved by locking the entire database file at the beginning of a
transaction.

Official site for SQLite http://www.sqlite.org/