Friendship: voluntary relationships between people who like and enjoy each other’s company. (McCornack, 382) (Relationships with) persons whom one knows, likes, and trusts. (MeSH)

Some friendships are based on wealth, power, or position. In these cases your friendship continues as long as your power, wealth, or position is sustained. There is another kind of friendship. Friendship based on … true human feeling, a feeling of closeness in which there is a sense of sharing and connectedness. This type of friendship is what I would call a genuine friendship. The factor that sustains a genuine friendship is a feeling of affection. (Dalai Lama, 99)

Agentic Friendships: voluntary relationships focused on achieving specific practical goals, such as those among peers in a study group or colleagues at work. (McCornack, 385)

Communal Friendships: voluntary relationships focused on sharing time and activities together. (McCornack, 383)

Friends With Benefits: friendships negotiated to include sexual activity without a commitment to deeper emotional bonds. (McCornack, 388)

Friendship Rules: guidelines for appropriate communication and behavior within friendships, such as keeping a confidence and showing support. (McCornack, 391)

Interpersonal Attraction: field of study within social psychology that asks the question ‘Why do people like one another; what factors contribute to attraction?’ (Bamford, 11/30/10) Any force that draws people together to form a relationship. (Floyd, G3)

Facial Symmetry: physical characteristic that contributes to the perception of attractiveness. If the face appears balanced and proportionate, there is likely to be an associated evaluation of attractiveness. (Bamford, 11/30/10)

Immediacy: behavior that increases perceptions of closeness between communicators. (Wood, 333) Nonverbal behavior that conveys attraction or affiliation. (Floyd, G3) As expressed in your posture, the degree to which you find someone interesting and attractive. (McCornack, 228)

Matching Hypothesis: suggests that people tend to be attracted to others with matching characteristics. (These include) age, cultural background, personal interests, religion, socioeconomic status, and “physical attractiveness.” Tendency of males and females of approximately equal physical attractiveness to select each other as partners. (Bamford, 11/30/10) For example, Michael dates Jennifer because she is pretty but not unapproachably gorgeous. (McCornack, 331)

Birds-Of-A-Feather Effect: a tendency to be attracted to others if we perceive them to have similar levels of physical attractiveness, values, and interests. (McCornack, 331) 

Similarity: (the principle that) people are often attracted to other people with similar characteristics, and relationships between people with similar interest and backgrounds produce less conflict. A factor commonly implicated in “interpersonal attraction.” (Bamford, 11/30/10)

Mere Exposure Effect: phenomenon where you feel more attracted to those with whom you have frequent contact and less attracted to those with whom you interact rarely. For example, the more June sees of Tom, the more attracted to him she becomes. (McCornack, 330)

Physical Attractiveness: attraction to someone’s physical appearance. (Floyd, G5) An important variable in interpersonal attraction. Attractive individuals are more likely to be evaluated positively than unattractive individuals. Likely to be perceived as honest, fun, happy, good in bed, smart, talented, and credible, whether they possess those characteristics or not. Conversely, unattractive people are likely to be perceived as slow, stupid, and unhappy whether they actually possess those characteristics or not. (Bamford, 11/30/10) Physical attractiveness is not correlated with "intelligence," mental health, or even "self-esteem." (Hockenbury, 441) 

Romance: an interpersonal involvement two people choose to enter that is perceived as romantic by both. For instance, Louise is in love with Robert, and Robert returns her affections. (McCornack, 326)