The phrase "wallpaper picker" refers to a tool or feature in a device or computer software that allows you to choose and change the background image or design on your screen. Full definition
Google's new wallpaper picker exists as a separate APK, meaning it can be installed without loading the Pixel launcher, and used with any Android home screen. (androidcentral.com)
There's also new Nexus Launcher - inspired folder designs and the ability to change the default wallpaper picker app. (androidauthority.com)
Other than the usual Marshmallow perks, the updated OnePlus X will also receive new icon packs, a new wallpaper picker as well as new apps, among other updates. (nashvillechatterclass.com)