Dung means animal droppings or waste. If you work at an elephant sanctuary, you're likely to spend a lot of time shoveling up elephant dung.
Dung is a tidy word for an untidy substance — animal poop. When farmers talk about cow dung or chicken dung, they'll probably call it manure instead. Some dung causes problems, like the runoff of pig dung into lakes and rivers, while other dung is used to help fertilize vegetable gardens. Dung is an Old English word, from a Germanic root — in Old High German, a tung was an underground room that was covered with dung for warmth.