OS X Mountain Lion: What is Bonjour?
Bonjour is a networking technology developed by Apple Inc. that makes it easy to set up and use devices and services on a network. Because Bonjour-compatible devices and services advertise their availability, it’s easy for you (or an application or service) to find devices and services that you want to use. For example, if you turn on file sharing, other OS X users on your local network will see your computer when they browse.
Bonjour requires Mac OS X 10.2 or later.