Final answer:
A stratus cloud that brings rain is called a nimbostratus cloud, which covers the sky uniformly and often brings prolonged precipitation.
Step-by-step explanation:
A stratus cloud which has become a rain cloud is known as a nimbostratus cloud. These clouds are characterized by their uniform gray color and can cover the entire sky like a blanket, often bringing continuous, light to moderate rain or snow. Unlike the high, wispy cirrus clouds made of methane ice crystals on Neptune or the fluffy, heaped appearance of cumulus clouds caused by convection, the nimbostratus cloud is lower in the atmosphere and lacks the well-defined structure seen in other cloud types.