Keri

Keri (קרי‎) is a Hebrew term which literally means "happenstance", "frivolity" or "contrariness" and has come to mean "seminal emission". The term is generally used in Jewish law to refer specifically to the regulations and rituals concerning the emission of semen, whether by nocturnal emission, or by sexual activity. By extension, a man is said to be a ba'al keri (בעל קרי‎) ("one who has had a seminal emission") after he has ejaculated without yet completing the associated ritual cleansing requirements.

The biblical regulations of the Priestly Code specify that a man who had experienced an emission of semen would become ritually impure, until the evening came and the man had washed himself in water; (Leviticus 15:16) any clothes or bits of skin which the semen came into contact with would also become ritually impure, until they had been washed in water and the evening had come. (Leviticus 15:17) The code adds that if the emission of semen occurred during sexual intercourse with a woman, then the woman would also become ritually impure, until the evening had come and she had washed herself in water. (Leviticus 15:18)

Non-traditional biblical scholars see these regulations as having originally derived from taboo against contact with semen, because it was considered to house life itself, and was thus thought of as sacred.

The Talmud adds prohibitions designed to avoid keri in cases that do not involve sexual intercourse. It was forbidden for a man to investigate himself to determine whether an emission of semen had occurred, on the basis that the sensation of touch causes keri (an oblique reference to masturbation); the Talmud goes on to address the concern that preventing any contact with the penis would make urination more awkward for males, and makes suggestions in this regard.

...
Wikipedia