The American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders (DSM V) has a comprehensive Narcissism Definition, which I share below.
I do find it confusing however. I don't see how any ordinary person could use this to decide if her mother is narcissistic. So while I include it here for the sake of completeness, I recommend instead reading the pages on Narcissism Traits and also Chris's amazing Characteristics Of Narcissistic Mothers.
The ASA's Narcissism Definition
To diagnose narcissistic personality disorder, the following criteria must be met:
A. Significant impairments in personality functioning manifest by:
1. Impairments in self functioning (a or b):
a. Identity: Excessive reference to others for self-definition and self-esteem regulation; exaggerated self-appraisal may be inflated or deflated, or vacillate between extremes; emotional regulation mirrors fluctuations in self-esteem.
b. Self-direction: Goal-setting is based on gaining approval from others; personal standards are unreasonably high in order to see oneself as exceptional, or too low based on a sense of entitlement; often unaware of own motivations.
2. Impairments in interpersonal functioning (a or b):
a. Empathy: Impaired ability to recognize or identify with the feelings and needs of others; excessively attuned to reactions of others, but only if perceived as relevant to self; over- or underestimate of own effect on others.
b. Intimacy: Relationships largely superficial and exist to serve self-esteem regulation; mutuality constrained by little genuine interest in others; experiences and predominance of a need for personal gain.
B. Pathological personality traits in the following domain:
1. Antagonism, characterized by:
a. Grandiosity: Feelings of entitlement, either overt or covert; self-centeredness; firmly holding to the belief that one is better than others; condescending toward others.
b. Attention seeking: Excessive attempts to attract and be the focus of the attention of others; admiration seeking.
C. The impairments in personality functioning and the individual's
personality trait expression are relatively stable across time and consistent across situations.
D. The impairments in personality functioning and the individual's
personality trait expression are not better understood as normative
for the individual's developmental stage or socio-cultural environment.
E. The impairments in personality functioning and the individual‟s
personality trait expression are not solely due to the direct physiological effects of a substance (e.g., a drug of abuse, medication) or a general medical condition (e.g., severe head trauma).