ECOSYSTEM IS EVERYTHING ABOUT THE HABITAT
Ecosystem is community of organisms, interacting with one another, plus the environment in which they live an with which they also interact. For example, lake, a forest, a grassland, tundra.
Such ecosystem includes all abiotic factors (non-living factors like temperature, rain fall, climate, pH, oxygen level etc) and biotic factors (living factors like predator, competitor, trophic levels, heights of trees, producers, consumers, decomposers etc.)
Knowing about a particular ecosystem is crucial to understand the animals in such habitat. So.. it is the biological term that is used to describe everything in the nature. The term ecosystem refers to the combined physical and biological components of an environment.