In contract bridge, an overcall is a bid made after an opening bid has been made by an opponent; the term refers only to the first such bid. A direct overcall is a bid made directly over the opening bid by right-hand opponent; an overcall in the 'last seat' (made over a bid by left-hand opponent and two subsequent passes) is referred to as a balancing overcall.
Read more about Overcall: Objectives, Suit Overcalls, Notrump Overcalls, Jump Overcalls, Other Overcalls, Responses To Overcalls