Lever is defined as a rigid bar (bone) that moves about an axis.

In psychology, the term lever can refer to a force or influence that is used to achieve a particular outcome or change. A lever may be physical (such as a lever on a machine) or psychological (such as a persuasive argument or an emotional appeal).

There are many ways in which the concept of lever is applied in psychology. For example, research on persuasion and influence may examine the ways in which different levers (such as logical arguments, emotional appeals, or social pressure) can be used to change people's attitudes or behaviors. In therapy, a lever might be a particular technique or intervention that is used to help a client make changes in their thoughts, feelings, or behaviors.

Examples of levers in psychology might include a therapist using a particular intervention to help a client overcome a phobia, or a politician using an emotional appeal to try to persuade voters. Understanding the role of levers in psychological processes can be an important aspect of research and theory development in psychology.