Ecology is best defined as the study of the inter-relationship between living organisms and the environment. It is the study of how organisms interact with each other and their surroundings, including both living and non-living components of the environment.
Ecology is a broad field that encompasses many different areas of study, including the study of populations, communities, ecosystems, and biomes. Ecologists examine the ways in which living organisms interact with each other and with their physical and chemical environment, as well as the ways in which human activities can impact these interactions.
By understanding the relationships between organisms and their environment, ecologists can develop strategies for conservation, management, and restoration of ecosystems. For example, ecologists can study the impacts of climate change on ecosystems, and develop plans to mitigate these impacts and help protect the biodiversity of our planet.
So, the correct answer is "the inter-relationship between living organisms and the environment."