off-hook - Computer Definition
A condition that exists when a telephone receiver or handset is lifted or removed from its cradle, thereby completing a circuit and placing the telephone in use. The term refers to the fact that early telephone handsets hung from a switch hook, a hook that activated a switch. See also on-hook.
The state of a telephone line that allows dialing and transmission but prohibits incoming calls from being answered. The phone is off-hook when the handset is lifted off the base of a stationary phone or when Talk is pressed on a portable phone. The term stems from the days when the handset rested on an actual hook. When it was removed, a spring caused contacts to press together, closing the circuit from the telephone to the switchboard in the central office (CO). When a handset is placed back on the base, it is said to be "on-hook," and the phone can receive a call. See central office.