What is the X in X-mas?
(Or "endless loop") Where a piece of program is executed repeatedly with no hope of stopping. This is nearly always because of a bug, e.g. if the condition for exiting the loop is wrong, though it may be intentional if the program is controlling an embedded system which is supposed to run continuously until it is turned off. The programmer may also intend the program to run until interrupted by the user. An endless loop may also be used as a last-resort error handler when no other action is appropriate. This is used in some operating system kernels following a panic.
A program executing an infinite loop is said to spin or buzz forever and goes catatonic. The program is "wound around the axle".
A standard joke has been made about each generation's exemplar of the ultra-fast machine: "The Cray-3 is so fast it can execute an infinite loop in under 2 seconds!"
See also black hole, recursion, infinite loop.