The Audio MIDI Setup utility is a program that comes with the Mac OS X

Mac OS X

Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...

 operating system for adjusting the computer's audio

Sound

Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...

 input and output configuration settings and managing MIDI devices.

It was first introduced in Mac OS X

Mac OS X

Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...

 as a simplified way to configure MIDI Devices. Previous to its inception, Open Music System

Open Music System

Open Music System is a virtual studio management application by Opcode for the Classic Mac OS. Similar to FreeMIDI by Mark of the Unicorn and Audio MIDI Setup by Apple, OMS is used to manage MIDI devices by providing applications and the Mac OS with information regarding the physical setup of MIDI...

(OMS) was commonly used for these tasks; a much more complicated and tedious system than AMS.