CD+G (CD+Graphics) is a special audio CD that contains graphics data in addition to the audio data on the disc. The disc can be played on a regular audio CD player, but when played on a special CD+G player, can also output a graphics signal. CD+G is most commonly seen used for karaoke and slideshows.
The Sega Saturn and Sega Mega-CD can both play CD+Gs. Non-Sega consoles which can play them include the Atari Jaguar CD, Philips CD-i, TurboGrafx CD, 3DO and Amiga CD32. Modern consoles don't support CD+G due to lack of demand for the feature.