Port and starboard are nautical terms for left and right, respectively. Port is the left-hand side of or direction from a vessel, facing forward. Starboard is the right-hand side, facing forward. Since port and starboard never change, they are unambiguous references that are not relative to the observer.
The term starboard derives from the Old English steorbord, meaning the side on which the ship is steered. Before ships had rudders on their centrelines, they were steered with a steering oar at the stern of the ship and, because more people are right-handed, on the right-hand side of it. The term is cognate with the Old Norse stýri (rudder) and borð (side of a ship). Since the steering oar was on the right side of the boat, it would tie up at wharf on the other side. Hence the left side was called port.