The text Intimate Relationships by Thomas Bradbury and Benjamin Karney at UCLA’s Marriage and Close Relationships Lab distinguishes among different types of social relationships:

  1. Interdependent relationship: A relationship in which the behavior of each participant affects the other. Interdependence is the defining characteristic of any social relationship.
  2. Personal relationship: An interdependent relationship in which the partners consider each other special and unique, rather than as member of a generic category (e.g. classmate or neighbor).
  3. Close relationship: A personal relationship in which the partners have strong, sustained mutual influence over a broad range of interactions.
  4. Intimate relationship: A close relationship that includes some kind of sexual passion that could be expressed and shared.

While these definitions are not universal, they do show the key dimensions of distinction for various kinds of relationships.