Hinge:
The folding part of the frame that connects the rim to the temples and allows the temples to lay flat along the inside of the frame.
Interchangeable Lens:
Lenses that can be swapped out of a pair of sunglasses to provide different looks or lens benefits.
Lens:
The transparent glass or plastic part of sunglasses that you looks through. Lenses protect your eyes by blocking UV light.
Lens Size:
The width of a lens in millimeters, measured at its widest point.