Sleep mode, sometimes called standby or suspend mode, is a power-sparing state that a computer can enter when not in use. The computer's state is maintained in RAM (random access memory). When the computer enters sleep mode, power is cut to any unneeded systems, while RAM receives just enough power to enable it to maintain data.
Most computers and computing devices are set to enter sleep mode after a certain period of inactivity. Laptop computers often enter sleep mode when they are closed. A computer usually wakes from sleep mode through touching a key, clicking the mouse or pressing the power button.