Homophily: This term describes the tendency for individuals to associate with others who share similar traits or interests - just like birds of a feather flocking together.
The theory that suggests individuals are attracted to others who are similar in physical attractiveness - akin to pairing socks based on color and pattern.
A perspective asserting that individuals derive part of their self-concept from their social group memberships - think about how wearing your school's colors at a football game makes you feel part of the team.