Always-on Display is a technology that displays your phone’s lock screen on the display at all times. It was first introduced by Motorola with its Moto X Pure Edition device in 2015, then Samsung brought it to their Galaxy S and Note lineups starting with the Galaxy S Active line of devices.
The benefit is convenience – you can see notifications without having to wake up or unlock your phone every time. The downside for some users is battery life since always-on screens tend to consume more power than a traditional AMOLED display would.
An Always-on Display screen is a screen coming up automatically when your phone has been inactive for some time. This screen allows you to check the date, view upcoming notifications, and read the weather condition without having to wake the device.