The version of Android originally on the device as supplied by the manufacturer or phone network, including any customizations, alternative interfaces and updates.
A "stock user interface" refers to a device with the default Android user interface. It lacks both manufacturer/carrier enhancements (e.g., Sense, BLUR) and customized ROMs from the mod community.
From the description, wouldn't vanilla-ui (which doesn't exist) be more appropriate? Or change the description?