Digital Smart Technologies for Amateur Radio is a protocol that describes the signaling and digital encoding of voice and data. It was developed by the Japan Amateur Radio League in conjunction with Icom. Though not required by the protocol, DVSI's AMBE vocoder is currently the only vocoder used to digitize audio.
Gateway systems connected to the internet allow D-STAR users to connect to another individual's station, another repeater, or a group of operators and stations (known as a "reflector").
See the Icom D-Star Equipment page. Also see the AOR DV-1 which decodes D-STAR.