I think HDMI is something everyone will be hearing a lot about in the future. HDMI stands for High Definition Multimedia Interface, although I like to think of it as DVI 2.0.
Like DVI, HDMI provides a complete digital video interface between devices. Unlike DVI, HDMI also carries digital audio (8-channel audio supported). The good thing about HDMI is that it is backwards compatible with DVI, and supports HDCP (High-bandwidth Digital Content Protection) to prevent copying of digital content.
There are already a few devices that have a HDMI connection, including plasma display panels and DVD players (some can even upscale DVDs to HD resolution), which produces excellent DVD playback quality, most likely due to the full digital path between the DVD disc and the display unit.
You can read the official HDMI FAQ here.