Programmer's key
The Programmer's Key, or interrupt button, is a button or switch on a computer which causes an asynchronous interrupt request (IRQ) to be sent to the processor. If a debugger is installed on the machine, it is activated when the interrupt request is processed, allowing the user to view and usually modify the computer's internal memory. This is quite useful in debugging software, which is why it gets its name.
On Macintosh computers, an interrupt request can be sent by holding down the command key and striking the power key on the keyboard.