"Power saving" refers to practices or technologies that reduce the amount of electricity or energy consumed by a device or system in order to minimize waste and improve efficiency.
You can choose from three different levels of battery savings in this mode, although I was unable to make the phone go into ultra power saving mode on its own at any moment. (sammobile.com)
Some of these apps even come with power saving features that help you configure device settings in order to maximize your battery life. (tomsguide.com)
There is also an ultra power saving mode which will disable everything except calls and messages. (androidauthority.com)