Organisms of many species are specialized into male and female varieties, each known as a sex. Sexual reproduction involves the combining and mixing of genetic traits: specialized cells known as gametes combine to form offspring that inherit traits from each parent. Gametes can be identical in form and function (known as isogamy), but in many cases an asymmetry has evolved such that two sex-specific types of gametes (heterogametes) exist (known as anisogamy).

Sex may refer to:

• Sex, the biological distinction of an organism between male, female or intersex, defined by the gametes it produces (or the reproductive organs it have), in anisogamous species
  • Mating types, a distinction of gametes, whether in anisogamous or isogamous species
• Sexing, the act of discerning the sex of an animal
• Sexual reproduction, a process of combining and mixing genetic traits, associated with the generation of new individuals, by means of meiosis and fertilization
  • Recombination, the process of mixing genetic traits solely, occurring both in organisms with sexual or asexual reproduction
• Animal sexual behaviour
  • Human sexual activity
  • Sexual intercourse, also called copulation or coitus
  • Non-penetrative sex, or sexual outercourse
• Gender, the distinction between male and female or masculinity and femininity within an individual's gender identity
• Human sexuality