Clouds that cover a large area are?

Clouds that cover a large area are called "stratus clouds".

Stratus clouds formed at medium or low rise; spread out layer upon layer covering a substantial zone As stratus mists thicken, precipitation for the most part covers over that area. Stratus Clouds are low clouds that create a dim, hazy veil with a uniform base all through the sky. They don't as a rule deliver precipitation, however sprinkle or snow grains are conceivable with stratus mists. One specific stratus cloud that influences transportation is fog.

Clouds that cover a large area are called stratus clouds.

Your answer is stratus clouds.