Participation in an "orgy" is a common sexual fantasy, and group sex targeting such consumers is a subgenre in pornographic films.
The term "orgiastic" does not generally connote group sex and is closer to the classical roots and this metaphorical usage.
ὄργιον, orgion) were ecstatic rites characteristic of the Greek and Hellenistic mystery religions.
Unlike public religion, or the private religious practices of a household, the mysteries were open only to initiates, and were thus "secret".
Because of their secret, nocturnal, and unscripted nature, the orgia were subject to prurient speculation and regarded with suspicion, particularly by the Romans, who attempted to suppress the Bacchanals in 186 BC.