Nominally, Virtual YouTubers (VTubers) are streamers who use an anime-style virtual avatar instead of a facecam. They don’t actually have to use YouTube as their streaming platform, or even do livestreams at all (VODs are fine, see Kizuna Ai).
One of the advantages of a virtual avatar is the separation of identity between the person on the inside and the VTuber persona (“kayfabe”).
VTubers who are especially focused on singing and music are usually called VSingers.