Omorashi - Piss desperation. Deriving sexual pleasure from individual(s) who have to pee extremely badly and are unable to get to an appropriate location to relieve themselves, often resulting in said individual(s) wetting themself.
Oral Sex - Sexual activity involving contact between an individual's mouth and another individual's genitalia.
Orgasm - The most highest point of sexual excitement after stimulation of the genitalia. Typically accompanied by involuntary actions such as ejaculation, vaginal contractions, and/or vocalizations.
Orgy - Group sex, typically in a party setting involving excessive alcohol consumption and at least five people.