A chick is a baby bird, especially a just-hatched chicken. Chicks are small, yellow, and fluffy.
Chick can describe most young birds, from an eagle chick to a flamingo chick, or be used more generally: "Dogs aren't allowed on the beach because of the nesting seabirds and their chicks." What most people picture when they think of a chick, though, is a newly hatched chicken, and in fact the word is a 14th century shortened form of chicken. It's also long been an informal, slightly offensive term for a young woman.