Research that involves the application of the behavioral and social sciences to the study of the actions or reactions of persons or animals in response to external or internal stimuli. (from American Heritage Dictionary, 4th ed)

Disciplines concerned with the study of human and animal behavior.

Critical and exhaustive investigation or experimentation, having for its aim the discovery of new facts and their correct interpretation, the revision of accepted conclusions, theories, or laws in the light of newly discovered facts, or the practical application of such new or revised conclusions, theories, or laws. (Webster, 3d ed)

The observable response an animal makes to any situation.