A switch on a telephone set that operates when the receiver is placed on the hook or removed from it.
Also called a "hook switch," it is the control mechanism that answers and hangs up a call on a telephone. When you place the handset in the telephone cradle, it depresses the switch hook's button and hangs up (puts the phone "on hook"). See off-hook and flash button.
With hundreds of thousands of calls attempting to get through, Luby had the following tip: "If you pick up your phone and don't hear a dial tone, don't hang up and don't hit the switch hook -- that will make the computerized switch think it has another call and you'll be placed in the back of the line.