Simple Definition:

Ecology is the study of how living organisms [living things like plants, animals, and bacteria] interact with each other and their environment.

For example, ecologists study how plants and animals depend on each other for food and shelter. They also study how pollution affects the health of ecosystems, like how oil spills harm marine life in the ocean.

Very Simple Definition:

Ecology is the study of how plants, animals, and other living things interact with their surroundings.

For example, ecologists study how animals find food and make homes in nature, and how pollution can hurt animals and plants.