1) Everything that an organism does, including covert actions like thinking. 2) Anything a person does that can be observed. 3) Anything an organism does. Although the definition is too inclusive as it stands, it cannot easily be restricted further (e.g., to activity of muscles or glands). For example, a shift of attention need not involve eye movements but qualifies as behavior. See also Specific cases. 4) That portion of an organism's interaction with its environment characterized by a detectable displacement in space through time of some part of the organism and that results in some change in the environment. A single behavior is called a response class. 5) Any directly measurable thing an organism does. Included are saying and doing, including physically functioning. In this book we use the term behavior synonymously with response and performance, and the term behaviors as an abbreviated way of saying "classes of behavior." 6) Any action of an individual. Operant behavior is behavior which "operates" on the environment, changing it in some way. 7) Broadly speaking, any activity of the organism; more particularly any activity which changes the position of the organism or any part thereof in space. The dependent variable in a science of behavior. 8) Any activity that passes the dead-man test. 9) A muscle, glandular, or electrical activity