Stratus means layer or blanket in Latin. A stratus cloud (St) is a cloud belonging to a class characterized by horizontal layering with a uniform base, as opposed to convective clouds that are as tall or taller than wide (these are termed cumulus clouds). More specifically, the term stratus is used to describe flat, featureless clouds of low altitude varying in color from dark gray to nearly white. A "cloudy day" usually features a sky filled with stratus clouds obscuring the disk of the sun. These clouds are essentially above-ground fog formed either through the lifting of morning fog or when cold air moves at low altitudes over a region. These clouds do not usually bring heavy precipitation, although drizzle and snow may occur.