An ecosystem is all the living things, from plants and animals to microscopic organisms, that share an environment. Everything in an ecosystem has an important role. Well, almost everything.
The term ecosystem was coined in 1935, though ecosystems have been around as long as living things. Eco is a spin-off from the word ecology and describes anything having to do with the environment and our relation to it. You've probably heard of related terms like eco-friendly and eco-warrior. And system comes from the Greek word systema or "organized body, whole."