What term describes a living thing?

The term that describes a living thing is "organism." An organism is any individual living entity that can react to stimuli, reproduce, grow, and maintain homeostasis. This broad definition includes everything from single-celled bacteria to complex multicellular organisms such as animals and plants.

In contrast, "species" refers to a group of organisms that can interbreed and produce fertile offspring, indicating a specific classification rather than an individual living entity. "Population" describes a group of individuals of the same species living in a particular area at the same time, and "community" refers to all the different species that live and interact in a certain environment. Each of these terms provides more context about relationships and classifications within biology but does not define what an individual living thing is.