ART stands for Android Runtime which is a method developed by the android development team for handling how the app runs . In ART , the apps are compiled and installed using the AOT (Ahead of time) compilation.

How to Switch to ART in Moto G (Android) device ?

To switch to the android runtime (ART) , you have to perform the following
1. Enable the Developer Options in your Moto G device .
This option is by default disabled or hidden in the device  , you can enable this option by navigating to Settings -> About Phone and the double tapping the Build Number 4 times (this might change sometimes).

2. Enable ART (Android runtime) from the Developer Options

After performing the first step , the Developer Options menu will be visible in the Settings App . In the Developer Options Screen , select runtime and from the options select ART.

You will be prompted to reboot your device , once that is done , your device would run in ART runtime.