Whats the device called on mountain bikes that prevents the chain from coming out of the chain ring?

No I’m not talking about the derailleur. I’m talking about that device that you see on mostly DH bikes near the front chain ring.

I’m trying to remember what this 3 wheel drifting electric bike is called or find something similar?

A while ago I road, in the parking lot of a dirtbike shop, a three wheel electric bike that looked like a tricycle , it’s back 2 wheels were plastic allowing for extremily fun drifts,but it had rubber wheels that came with it. I sorta recal It might be called something like ” spin e” [...]