SQLite is a small mobile database engine…not mobile as in cellular; mobile as in you can take the database file and copy/move it to any other box with sqlite libraries and use it. The database file can (and should) reside within the same directory structure as the application using it, unlike most database engines where all database files reside in the database server directory structure. This makes your entire application easily transferrable and installable (no need for database setup). Of course, it’s nowhere near as powerful as most database engines but for small applications or dynamic configurations, this kind of database works great.
Here’s a nice article and short tutorial on using PDO and SQLite: