Launcher is the name given to the part of the Android user interface that lets users customize the home screen (e.g. the phone's desktop), launch mobile apps, make phone calls, and perform other tasks on Android devices (devices that use the Android mobile operating system). Launcher is built into Android, however there are a number of Launchers available for download in the Android Market.
See Tweak Your Android Homescreen with Customized Launchers and Android Codenames to learn about updates for the open source Android mobile operating system.
See also Essential Android Security Apps in Webopedia's Quick Reference section.