A utility program to ease the installation of another, probably larger, application. It is also possible for hardware to have an installer accompany it, to install any low level device drivers required.

The installer commonly asks the user to enter desired configuration options for the main program or hardware, and sets up various initialisation files accordingly, as well as copying the main program to a hard disc.

Some badly designed operating systems require applications to provide an uninstaller because of the number of different files modified or created during the installation process.