Major ritual impurity in Islam. A believer enters this state when, if male:

  1. sperm exits from him;
  2. or the head of his penis enters a vagina.
For a female, this condition occurs when:
  1. sexual fluid exit from her;
  2. the head of a penis enters her vagina;
  3. after her menstrual period;
  4. after her postnatal lochia stops or after a child is born in a dry birth
The Arabic term for sexual fluid (maniyy) refers both to the wetness of the female and the semen of the male which are emitted during orgasm.

A person in this state may not recite any part of the Qur'an, unless unintended, and may not enter into a masjid except to pass through it. All the prohibitions for those with minor ritual impurity (which requires wudu) applies to those in this state as well. One must perform the ghusl to purify oneself from this state.

Information from Reliance of the Traveller.