Muddiness is the sloppy, damp, dirty state of wet earth. You can also use muddiness for confusion or vagueness: "The muddiness of the writing made that book impossible to finish."
You can use this noun for the muddy ground beside a pond — its muddiness might make you decide to run home and grab your boots. Figuratively, muddiness describes anything that's vague or unclear, like the muddiness of your friend's logic in her hastily written essay. Sometimes sound is described this way too, if it's undefined or blurry: "I'm not a fan of that dissonant muddiness. I like songs I can sing along with."