POC Proof of Concept 
Typically a benchtop, or hacked-together, prototype that exhibits the primary or critical functionality of the product. These are never meant to look pretty but are instead used to understand technical feasibility and project risk.
FP Functional Prototype 
An array of sub-systems brought together into a works-like prototype for market research, functional testing, or early fundraising. Not all the sub-systems or features will be represented at this point but the important ones will be.
EP Engineering Prototype 
The primary sub-systems are integrated into a coheseive works-like prototype, incorporating some or all of the looks-like aesthetics of the product. User testing, design validation, and investor pitches are common uses.
