- "Oh, baby."
- —Emily Young engaged in 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.
In 2353, Vala Mal Doran had sex with Typhuss James Halliwell after they met in a night club. In 2354, Samantha Carter had sex with Typhuss James Halliwell after they met in a bar. In 2360, Samantha Carter was so lonely that she had sex with Typhuss James Halliwell in her quarters at Stargate Command. Later Samantha told Typhuss that the only reason she had sex with him was that she was lonely snice their divorce a year before. In 2370, Helen Magnus and Typhuss James Halliwell went on vacation with each other to Risa. Helen Magnus had sex with Typhuss James Halliwell several times while on Risa.
In 2377, after Typhuss returned to Earth, Samantha Carter and Typhuss James Halliwell went on vacation with each other to Risa. Samantha Carter had sex with Typhuss James Halliwell several times while on Risa.
In 2378, Kira Nerys first met Typhuss James Halliwell on Deep Space 9. Typhuss and Kira soon showed an attraction to each other. Typhuss got authorization from Kathryn Janeway and The Doctor to engage in a romantic relationship with Kira Nerys. Kira took Typhuss back to her quarters and had sex with him.
In 2381, Matthew Scott and Vanessa James had sex in a closet in Icarus Base. Later that year, Colonel Everett Young (while in the body of Colonel David Telford) had sex with his wife Emily Young via the Ancient Long-range communication device. Due to Destiny dropping out of FTL while this was transpiring, Colonel Telford momentarily switched back to his own body in the middle of intercourse, leaving him utterly shocked.