To have an “identity crisis” is to become unsure of what sort of person, in some deep and fundamental sense, one is.

 To have an “identity crisis” is to become unsure of what one’s most characteristic properties are—of what sort of person, in some deep and fundamental sense, one is. This “personal identity” contrasts with ethnic or national identity, which consists roughly of the ethnic group or nation one takes oneself to belong to and the importance one attaches to this.

One’s personal identity in this sense is contingent and temporary: the way I define myself as a person might have been different, and can vary from one time to another. It could happen that being a philosopher and a parent belong to my identity, but not being a man and living in Yorkshire, while someone else has the same four properties but feels differently towards them, so that being a man and living in Yorkshire belong to his identity but not being a philosopher or a parent. And these attitudes are all subject to change.