What is a compost pile and why might I want one?

Annette, A compost pile is a place that you have outside somewhere in your yard, where you put your organic waste that you would normally throw away. Stuff like your lawn, garden waste, and your food waste also. Basically, you let it decompose and then you use it as fertilizer in your yard. I don't do that but, some people who are really into gardening do.