What does UV stand for?

What does UV stand for? as in uv texture or uv coordinates. I know how to use uv textures and unwrap I am just curious about the abbreviation.

I think U and V are the coordinates of the texture on the object. Not sure why they’re called U and V though.

In simple terms, X,Y,Z are spacial co-ordinates while U,V,W are surface/mesh co-ordinates.