Determine about the three-state gate

A three-state gate is a digital circuit which shows three states. Two of them are equivalent to logic 1 and 0.  The third one is a high impedance state.  The  high-impedance  state  acts like  an  open  circuit,  which  means  that   output  is disconnected and does not have a logic significance. The one most generally used in design of a bus system is buffer gate.

The graphic sign of a three state buffer gate is shown in figure given below. The control input determines output