SysRq

System request (often abbreviated SysRq, SysReq?, Sys Rq or Sys Req) is a key on keyboards for PCs that has no standard use. This key can be traced back to the operator interrupt key used on IBM 3270-type console keyboards of the IBM System/370 mainframe computer, which was used to cause the operating system such as VM/370 or MVS to allow the console to give input to the operating system.

In Linux it is used for Raising Skinny Elephants