Connected Standby is a device operating mode for Windows in which a device can remain in a low-powered, idle condition but can still be transitioned immediately to a fully operational state.
Connected Standby enables a Windows on ARM (WOA) powered processor to consume minimal battery power when it is not being used and/or its display is off.
Techopedia explains Connected Standby
Connected Standby mode is primarily a device’s battery operating mode on the Windows operating system. In this mode, the device is turned on, but the display will be dark. Windows suspends all applications that may be running and puts the device in a state that consumers minimal power. When a user punches a key or touches the screen, the device instantly becomes operational.
Connected Standby differs from sleep mode in its ability to instantly transition between an off-screen standby to an on-screen online mode.