Someone who doesn't want to show their
face on stream so they instead use an
animated anime character that "talks" whenever they talk. It's a smart alternative rather than not showing their face at all (as it attracts more viewers).
User A: You should check out Insert
streamer here, she has this totally cute
anime character on-screen that talks whenever she talks! It's so cute!
User B:
Oooo, sounds like you found a Vtuber!
User A: Vtuber? Didn't know they had a name.