Back (bk), n. [AS. bæc, bac; akin to Icel., Sw., & LG. bak, Dan. bag; cf. OHG. bahho ham, Skr. bhaj to turn, OSlav. bg flight. Cf. Bacon.] 1. In human beings, the hinder part of the body, extending from the neck to the end of the spine; in other animals, that part of the body which corresponds most nearly to such part of a human being; as, the back of a horse, fish, or lobster.