A pearl necklace is a colloquial term describing the sex act where a man ejaculates onto the chest, neck, or breasts of his partner. The term originated from the fact that the drops of semen can look like a string of pearls around a person’s neck.
The term first entered the mainstream when ZZ Top released the song "Pearl Necklace" in 1981. It did not gain widespread popularity, though, until it was explained in a 2004 episode of the HBO comedy Sex and the City.