From Memetics

In psychology, identity is the qualities, beliefs, personality, looks and/or expressions that make a person (self-identity) or group Categorizing identity can be positive or destructive.

A psychological identity relates to self-image (one's mental model of oneself), self-esteem, and individuality.

In the term of memetics an identity is a central meme that has a core and substantial influence over the other competing memes on a host.

See Wikipedia - Identity (Social Sciences)