Sambunmi3 did a great job describing them there, and the definition is very close to the one provided by the DSM - 5.
The DSM also lists these personality disorders so examples might include:
Narcissistic personality disorder
Antisocial behavioural personality disorder
Borderline personality disorder
Obsessive-compulsive personality disorder
There are many many more. But one can see how they match the definition.
Another feature of a personality disorder is that the thinking or behavior that is associated with the disorder tends to stick around or stay with the individual over a sustained period.
Another important criterion according to the DSM - 5 is that these 'general' personality disorders are pervasive across a wide range of different social situations.
The field of personality disorders is huge, and there tends to be more than one model to explain its presence/classification.
@Daniel Sumner a big thanks for providing more clarity... The field of personality disorders is huge indeed.
Personality disorders are long-term patterns of behavior and inner experiences that differs significantly from what is expected. The pattern of experience and behavior begins by late adolescence or early adulthood and causes distress or problems in functioning.