Ask ten people what prototyping is and you should get ten different answers, or they'll say it's a click through using Invision.
Prototypes can be as little as two bits of paper with scribbles on it all the way to a full product (Heck, they can even be videos of animations). It's a broad umbrella term that requires goals, smarter goals. A prototype should only be as useful as the hypothesis it is trying to prove/disprove.
Because of this you need too be well formed in how best to create the prototypes that would need to be made. When we need to make a paper prototype, I'm there for it. When We need to test out a minute feature of a larger product, I'm there. When you need to have a full application created that mimics real world use, I am there.