1A frill of material at the neck of a garment, a ruff.

2Palaeontology an upward-curving bony plate extending behind the skull of many dinosaurs, chiefly ceratopsians.

3Zoology the erectable folds of skin on the neck of the Australian frilled lizard, Chlamydosaurus kingii (family Agamidae), which are raised in threat displays and for thermoregulation.