Quick Time is "a package of system-level code, with C and Pascal programming interfaces, that higher-level software can use to control time-based data"; it supports oodles of different formats of movies, audio, images, animations, etc. It it made by Apple, and is available for Mac and Windows. It includes a player application which is a competitor of sorts to Real Player, Microsoft Media Player, etc.
Quick Time was the first major attempt ever at storing digital video in a not-too-terribly proprietary format. It has been around since at least 1991 ("Friends of Quick Time" is celebrating Quick Time's 10th anniversary. See www.friendsoftime.org 
).
Quick Time also has a very nice timing kernel inside of it. There were reports that a miller was using Quick Time to control the milling machines.
See original on c2.com