Personality refers to individual differences in characteristic patterns of thinking, feeling and behaving. The study of personality focuses on two broad areas: One is understanding individual differences in particular personality characteristics, such as sociability or irritability. The other is understanding how the various parts of a person come together as a whole.

Personality can be defined in different ways, depending on whether we focus on the individual or on people in general.
If we focus on people in general, then we can define personality in terms of individual differences — that is, the range of different styles of thinking, feeling and acting.

Just as human beings can differ a great deal in terms of their physical traits (height, weight, hair, and so on), they also differ in terms of mental and behavioural traits. For example, some people are noticeably talkative and outgoing while others are noticeably quiet and reserved. Such differences and variations are seen everywhere throughout the human population.

If we focus on the personality of a specific individual, we can define it as that person’s particular set of enduring dispositions or long-term tendencies to think, feel and act in particular ways.

We’re not talking about specific actions being repeated again and again, like compulsive hand-washing, but about overall patterns, tendencies, inclinations. Someone who has tended to be quiet and reserved up to now will probably still tend to be quiet and reserved tomorrow. That doesn’t necessarily mean that they are compelled to be quiet and reserved at all times, in every possible situation. Rather, they are disposed to be quiet and reserved more often than not.

Questions of personality have vexed mankind from the dawn of personhood: can people change? How do others perceive me? What is the difference between normal and pathological behavior? One's personality is so pervasive and all-important that it presents a clinical paradox of sorts: it is hard to assess our own personality, and impossible to overlook that of others.