A basic biology definition would be is that it is the study of living organisms. It is concerned with all that has life and living. (Ref.1) In contrast to inanimate objects, a living matter is one that demonstrates life. For instance, a living thing would be one that is comprised of a cell or a group of cells.
Each of these cells can carry out processes, e.g. anabolic and catabolic reactions, in order to sustain life. These reactions may be energy-requiring. They are also regulated through homeostatic mechanisms. A living matter would also be one that is capable of reacting to stimuli, adapt to its environment, reproduce, and grow.
The major groups of living things are animals, plants, fungi, protists, bacteria, and archaea. Biology studies their structure, function, distribution, evolution, and taxonomy.