A fold of skin that covers and protects part of the eyeball. Examples: upper eyelid, lower eyelid, nictitating membrane.
Comment:
[taxon-note] "In humans the upper and lower eyelid consists of the following layers, starting anteriorly: (1) skin, (2) a layer of subcutaneous connective tissue, (3) a layer of striated muscle fibres of the orbicularis muscle, (4) a layer of submuscular connective tissue, (5) a fibrous layer, including the tarsal plates, (6) a layer of smooth muscle, (7) the palpebral conjunctiva."