A piece of material used to cover or protect a wound, an injured part, etc.: a patch over the eye.
A piece of sticking plaster with a substance on it, which is stuck to the skin to allow the substance to be gradually absorbed into the system through the skin, e.g. in HRT.
A non-elevated skin lesion larger than 1 cm in diameter.
A small circumscribed area distinct from the surrounding surface in character and appearance.