What exactly is it? The simple explanation: "being aroused by the idea of having sex with someone sleeping," whether actual sexual contact occurs or not, said Dr. Michael First, a professor of clinical psychiatry at Columbia University Medical Center.
To be clear: As far as is known, Cosby has not been diagnosed with this or any other psychological disorder. First has not treated the comedian, has no direct knowledge of him, and just discussed somnophilia (som-no-FILL-ee-uh) in general.
The term came up Wednesday in a motion filed by a lawyer for Andrea Constand, the first woman to accuse the actor-comedian of sexual assault, seeking to force disclosure of more records in her previously settled case. Cosby acknowledged in a 2005 deposition in the case that was unsealed this week that he obtained quaaludes to sedate women he wanted to have sex with.
"Although some of the women engaged in consensual relations with Cosby, their accounts substantiated defendant's alleged predilection for somnophilia," Constand's lawyer, Dolores Troiani, wrote in the motion.
So why might someone be turned on by the thought of sex with someone who is out of it?
"The research on this is very, very limited," First said. "It's possibly that what the person might find arousing is the idea you have full control over this person," or it could be the lack of consent, the sense of getting away with something, or even just the attraction of seeing the person asleep, he said.
Somnophilia is one of the 250 recognized "paraphilias" — abnormal or uncommon sexual conditions. But what is kinky to one person may not be to another.
"Sexual tastes have gotten so much broader or better accepted, it's really hard to say what's normal or not," First said.
Most people agree that pedophilia (sexual attraction to children) and necrophilia (attraction to dead bodies) are not normal. Only eight paraphilias are in the Diagnostic and Statistical Manual of Mental Disorders, the main guidebook psychiatrists use, and somnophilia is not among them.
That's partly because it is so uncommon, First said.