QuickTime is the name of the software designed by Apple for playing audio and video files. QuickTime is the default media player on Mac computers, much like Windows Media Player on Windows machines.
Quicktime is used by Mac OS X and applications including QuickTime Player, iTunes, and Safari (via the QuickTime browser plug-in) to play video, sound, and image files. In fact, Quicktime is the foundation on which the popular iTunes software and iPod technologies are built.
However, if you own the iPod portable media player, you most likely have QuickTime installed, because QuickTime is the media playback engine for iTunes, the software used to manage files on the iPod. Keeping the software on your computer updated is an important part of the maintenance process, and you can check for updates for the QuickTime player using the built-in software update utility.