Wiktionary
n. (context computing English) the state of a computer system (especially a laptop), in which the screen and hard drive are switched off, and the only task running monitors external activity (such as a key press) which restores the system to its active state
Wikipedia
Usage examples of "sleep mode".
She was out just long enough to trigger her computer's downtime activation, and though the screen was blank, in the auto-sleep mode, the hard drive started turning, and silently activated the onboard modem.
From now on, it would only send new ones -- which would make for much shorter and faster transmissions -- but only in the evening, and only after ninety-five minutes of total inactivity on the computer, and only when it was outwardly in auto-sleep mode.
When he touched the trackball, the hundred-centimeter display awoke from Sleep mode, throwing enough light onto the desk for him to see his split keyboard - an antique accessory that required an arcane skill, but still Greene's first choice for talking to his system.
To fall asleep is to relax sufficiently so that can occur and surrender into the sleep mode: same sort of process.
She nodded, clicking her computer into sleep mode and sitting back to watch me.