Think of each room or area in the house as a zone, it could be a living room, patio, kitchen or even a closet or bathroom. Each zone can be individually controlled in terms of volume and what you wish to listen to.
Some examples of sources are AM/FM radio, satellite radio, CD/DVD, iPod, computer or media server.
Speakers can be as prominent (, ) or discreet (//) as you like.
Distributed audio systems can be as small or large as you need them to be. They can be tailored to budget, sound quality, loudness or any combination of the 3.