Sex

Sex can refer to gender, or the act of intercourse or acts leading up to, or following, intercourse, including if intercourse is not achieved or is not desired.

Virginity is the state of never before having had intercourse.

On Earth, human sexuality varies. Heterosexuality refers to a preference for the opposite sex, e. g. males for females, and vice versa. Homosexuality refers to a preference for the same gender, e. g. females for females. Bisexuality is attraction to both genders. Intersex individuals can show more than one set of genitalia, or can just have less specific internal organs. An individual who is transgendered does not personally identify with their original biological gender. An open marriage generally refers to a marriage where the parties are free to engage in intercourse with others.

Slang for any of these terms, including homosexuality, varies greatly over time. Acceptable slang in one decade may become a slur in the next, or the reverse might occur. Gay is a generally-accepted umbrella statement for homosexuality, often referring more to men, though the term is sometimes used to refer to women. Gay women are generally referred to as lesbians. Coming out refers to the act of informing others of one's sexuality. The condition of being closeted refers to keeping one's sexuality a secret.

Sexuality varies among species. Denobulans have three mates of the opposite gender, and each of these mates has three, etc. Andorian marriages require groups of four.

While preferences are not specified, the presence of such multiple individual marriages strongly implies that some sexuality may be fluid.

Sexology is the scientific study of sexuality. Both Lyrans and U'lanna considered sexology as a medical specialty.