1. The branch of the biological sciences that deals with the relationship between organisms and their environment, including their relationship with other organisms.
2. The science concerned with interactions between organisms and the environment on spatial scales ranging from parts of individuals to the biosphere as a whole.

Literally, ecology means the "study of houses". The word was coined as ökologie by Ernst Haeckel, a German zoologist, in the 1870’s, based on the Greek word oikos. Although this means “house”, Haeckel was using it in the wider sense as “dwelling, habitat”. It was adopted into English soon after its coinage, originally as oecology which is similar to a Latin form.

Ecology has been divided into four major sub fields:

• Physiological ecology, concerned with interactions between individual organisms and the environment.
• Population biology, the regulation of population growth and population size, and interactions among populations.
• Community ecology, characteristics of the collective properties of the organisms in an area.
• Ecosystem ecology, regulation of the flows of energy and material in terrestrial and aquatic ecosystems.