Mecha (メカ - meka) are giant robots, vehicles, construction equipment, mobile buildings and generally over-sized machines. Short for "mechanical", but is unrelated to the tag mechanical.
Power suit - Suit that protects the wearer and/or enhances their abilities, without covering the user entirely.
Power armor - Similar to a power suit, it also covers the pilot entirely in similar fashion to body armor.
Exoskeleton - Small mecha without a covered cockpit that's worn like a power suit rather than piloted
Walker - A type of walking mecha that usually lacks arms.
Mecha - Giant (usually anthropomorphic) robots. Can be piloted or not. Some of them even transform into vehicles.