A same-sex relationship is a relationship between persons of the same sex and can take many forms, from romantic and sexual, to non-romantic homosocially-close relationships. The term is primarily associated with gay and lesbian relationships. Same-sex marriage refers to the institutionalized recognition of such relationships in the form of a marriage; civil unions may exist in countries where same-sex marriage does not.
The term same-sex relationship is not strictly related to the sexual orientation of the participants. As people in the bisexual-polysexual-pansexual, queer, asexual and also heterosexual spectra may participate in same-sex relationships (particularly depending on the legal, social and scientific definition of sex, that often erases the birth gender assignment-diverging identities of binary and genderqueer/non-binary trans people and those of ethnic genders alike), some activists claim that referring to a same-sex relationship as a "gay relationship" or a "lesbian relationship" is a form of bisexual erasure.
The lives of many historical figures, including Socrates, Alexander the Great, Lord Byron, Edward II, Hadrian, Julius Caesar, Michelangelo, Donatello, Leonardo da Vinci, Oscar Wilde, Vita Sackville-West, Alfonsina Storni and Christopher Marlowe are believed to have included love and sexual relationships with people of their own sex. Terms such as gay or bisexual have often been applied to them; some, such as Michel Foucault, regard this as risking the anachronistic introduction of a contemporary construction of sexuality foreign to their times, though others challenge this.