Introduced In: 10.0 "Cheetah" (2001) 

Like a lot of Mac OS X's features, the Dock was first seen in the NeXTSTEP and OpenStep operating systems. The Dock introduced an easy way for users to launch their favorite or most-used programs. Throughout the years, the Dock's functionality has grown to where it's hard to imagine not using it. Apple's mobile OS, iOS, even incorporated a version of the Dock. That little bar at the bottom of your iPhone and iPad? Yeah, that's a Dock.