Definition - What does Kill Switch mean?
A kill switch is a form of safety mechanism used to completely shut off a device in case of an emergency situation where it cannot be shut off using the normal process or if immediate shut off is required. This has traditionally been used in factories and industrial facilities to shut off the system in case of emergency. To make the switch visible to everyone, it often appears as a "big red button."
In the digital age, a kill switch does essentially the same thing, only it is not normally a physical switch, but a software implementation used to disable an application that has an expired license or disable a stolen device like a cell phone.
Techopedia explains Kill Switch
A kill switch, as the name implies, is a switch that can kill or disable something, be it be a production line, a complicated nuclear power system or a consumer device like a cell phone or tablet. Its function is as a safety mechanism or an emergency stop to whatever process is happening. Physical safety is its function in industrial environments such as factories where large machinery operates and can potentially malfunction, and it is especially useful if a worker is in danger.
In digital devices, a digitally implemented kill switch is used to protect data by either erasing it or permanently or temporarily disabling the device, rendering it unusable by the thief without unlock credentials from the owner. As cell phones become more technologically advanced and expensive, they have become the target of an increasing number of thefts. A kill switch built into the OS of the phone or as third-party apps have been proposed to discourage theft by rendering the devices unusable and ultimately worthless. Authorities believe that this would make them less of a target for theft if they become worthless immediately afterward.