In my 25 years working as a programmer or electronic engineer, I've never heard that phrase used in a computer context.

something that automatically kills power to whatever appliance it is hooked up to. Pretty simple.....

A kill switch (also called an e-stop) is a security measure used to shut off a device in an emergency situation in which it cannot be shut down in the usual manner. Unlike a normal shut down, which shuts down all systems naturally and turns the machine off without damaging it, a kill switch is designed to completely abort the operation at all costs.

A kill switch is a mechanism used to shut down or disable machinery or a device or program. The purpose of a kill switch is usually either to prevent theft of a machine or data or as a means of shutting down machinery in an emergency. In manufacturing, for example, a kill switch (also called a big red button) might be used to shut down machinery if a worker is in danger. In mobile computing, a kill switch can disable a device that has been reported lost or stolen. By activating a kill switch, the network administrator can protect the data on the device from being stolen or altered. In a car or boat, a kill switch can prevent the vehicle from starting unless an associated security mechanism is activated. Software programs sometimes include encoded kill switches as anti-piracy mechanisms. Microsoft's Vista operating system and related products include a component that some industry experts are calling a virtual kill switch. After installing the software, a user has 30 days to successfully register the product. If the user fails to enter a valid registration key before the deadline passes, the software will operate in what Microsoft is calling "reduced functionality mode:" The background goes black. There is no start menu. There are no desktop icons. Users are automatically logged out of Web browsers after one hour. Kill switches are also used for a wide variety of machinery both inside and outside the IT world, including car ignition systems, boat motors, industrial machines and gas pumps. A kill switch for vehicles and machinery is sometimes called a "dead man's switch" because its purpose is to shut the vehicle or machine down if the operator becomes incapacitated.