Concise Bible Dictionary:
In the Old Testament it is the skin of grapes (Num. 6:44All the days of his separation shall he eat nothing that is made of the vine tree, from the kernels even to the husk. (Numbers 6:4); see 2 Kings 4:4242And there came a man from Baal-shalisha, and brought the man of God bread of the firstfruits, twenty loaves of barley, and full ears of corn in the husk thereof. And he said, Give unto the people, that they may eat. (2 Kings 4:42), margin). In the New Testament it is κερἀτιον, which is the fruit, not the husk, of the carob tree. It is abundant in Syria, and the pods, containing a sweet pith-like substance, are food for cattle and pigs: it is occasionally eaten by the very poor. It is also termed “St. John’s Bread,” owing to the tradition that John the Baptist used its fruit in the desert. Quantities of the pods are imported into England under the name of locust beans, and used as food for horses (Luke 15:1616And he would fain have filled his belly with the husks that the swine did eat: and no man gave unto him. (Luke 15:16)).
Carob tree (Ceratonia siliqua) with fruit.