I've been looking at the FindPartOnRay function for a Ray Cast and when going over it I noticed that is mentioned that it returned something called a Surface Normal. I've looked around and I've seen it referenced in other questions on other sites but I haven't found an actual explanation of what it is and what can be done with it.
Fancy word for look-direction of a particular part face, like lookVector. Since raycast always hits a particular face there is a particular normal.
Non-rotated part's top surface normal is (0,1,0). Of course it can actually be anything, given any rotation.