is a 接尾後（せつびご） (suffix) that is used in Japanese to express when one thing is ‘covered in’, or ‘filled with’ another thing.
will be attached to the end of nouns, before (sometimes) being followed by the 格助詞（かくじょし） (case marking particle) の and a second noun. The second noun is frequently omitted if the place or thing that is ‘covered in’ something is obvious.
The underside of this pancake is covered in holes so it is gross.
This park is covered in garbage, so I don't want to bring my kids here.
I don't want someone to see me drive a car covered in scratches, so I always drive my wife's car.
Don't put mud-covered shirts in the washing machine!
is primarily used to express things that exist in a ‘scattered’ state (like stars in the sky). Due to this, it will not sound natural when used to describe a thing that is ‘covered in’ something that is not scattered in some way.
Please cover my wall with white paint. (Unnatural, unless the speaker specifically wanted paint speckled, rather than covering the wall)
I took my blood-covered shirt to the dry cleaner. (Natural, as blood drops may be scattered)