In their opus magnum "Personality Disorders in Modern Life", Theodore Millon and Roger Davis define personality as:
"(A) complex pattern of deeply embedded psychological characteristics that are expressed automatically in almost every area of psychological functioning." (p. 2)

The Diagnostic and Statistical Manual (DSM)) IV-TR (2000), published by the American Psychiatric Association, defines personality traits as:

"(E)nduring patterns of perceiving, relating to, and thinking about the environment and oneself that are exhibited in a wide range of social and personal contexts." (p. 686)

Laymen often confuse and confute "personality" with "character" and "temperament".

Our temperament is the biological-genetic template that interacts with our environment.

Our temperament is a set of in-built dispositions we are born with. It is mostly unalterable (though recent studies demonstrate that the brain is far more plastic and elastic than we thought).

In other words, our temperament is our nature.

Our character is largely the outcome of the process of socialization, the acts and imprints of our environment and nurture on our psyche during the formative years (0-6 years and in adolescence).

Our character is the set of all acquired characteristics we posses, often judged in a cultural-social context.

Sometimes the interplay of all these factors results in an abnormal personality.