The term 'stratus' is a type of CLOUD formation that is characterized by its flat, layered appearance. It is usually composed of low-level clouds and can be seen in the sky as a grayish-white sheet. Stratus clouds are typically found at altitudes between 6, 500 and 20, 000 feet and are often associated with fog or light rain. They are also known to produce a halo effect around the sun or moon when the sun's rays pass through them.