What is the name for stopping on snow skis technique?

Answer 1

It depends on how you do it. If you point the tips towards each other, it is called plowing, though when taught to beginning kids it is sometimes referred to as the 'Pizza stop'.

I'm not sure what it is called if you just slide sideways. I just call it stopping.

When you "slide" sideways it's called hockey stopping. It is actually much more effective at even slightly higher speeds. Snowplowing (same as plowing, just a different name) can really hurt your knees. I have a cousin who is just about to turn 14 but she has to wear knee braces skiing because she snowplows at high speed way too much.