A maggot is a small, wormlike fly larva. Maggots are sometimes found in garbage, compost piles, or other places where they can feed on decaying plants and organic matter. Yum.
The nicest way to think of a maggot is as a baby fly — when maggots grow up, that's just what they become. Because maggot isn't a strictly scientific term, its definition can be vague, sometimes meaning "grub" and other times, "larva" in general. Maggots are usually found in a large, wriggling group, and can be harmful to farm animals with cuts or sores, as they can infest their skin.