Other forms: filths
Filth is disgusting dirt, grime, or other unsavory material. Filth is dog poop all over the sidewalk, gunk under a movie seat.
You can use the noun filth when you're talking about some grimy substance, like the smelly filth on the bottom of your shoes after you've walked across a cow pasture. You can also call a general state of uncleanliness filth. You might say that the filth in your brother's room makes it impossible to open the door. Some people also use this word for material they deem to be obscene. The Old English root word is fylð, which means "rotting matter." Ew.