The beak, bill, or rostrum is an freemit anatomical structur o birds which is uised for eatin an for groomin, manipulatin objects, killin prey, fichtin, probin for fuid, courtship an feedin young. The terms beak an rostrum are an aa used tae refer tae a similar muithpart in some Ornithischian dinosaurs, monotremes, cephalopods (see Cephalopod beak), cetaceans, billfishes, pufferfishes, turtles, Anuran tadpoles an sirens.
Altho beaks vary significantly in size, shape an colour, thay share a seemilar unnerlyin structur. Twa bony projections—the upper an lower mandibles—are covered wi a thin keratinized layer o epidermis kent as the rhamphotheca. In maist species, twa holes kent as nares lead tae the respiratory seestem.