Rape pornography features performers simulating rape. The term BDSM dates back to 1969; however, the origin of the term BDSM is unclear and is believed to have been formed either from joining the term B&D with S&M , or as a compound initialism from B&D, D&S , and S&M. A survey by the New York City Department of Health and Mental Hygiene found that heterosexual women are more likely to bareback when engaging in anal sex than homosexual and bisexual men. It is used, for example, at fertility clinics to stimulate sperm donors. Such ejaculation can be done by mammary intercourse, or masturbation over the other person, or result from the withdrawal of the penis from a partner mouth as he is ejaculating following fellatio, irrumatio, or intercourse. Transsexual pornography is a genre of pornography. Group sex pornography features at least two men and two women , usually more, who all perform sex acts on each other. In gay hentai Japanese, this natural-fibre rope is known as asanawa; the Japanese vocabulary does not make a distinction between milf xxx hemp and jute. Types of anal sex can also be a part of lesbian sexual practices. It is geared towards heterosexual men, who most typically define a threesome as such. The cover can have gay bear porn hinges or be a separate part. Some women who engage in same-sex sexual activity may reject not only identifying as lesbians but as bisexual as well, while other women self-identification as lesbian may not align with their sexual orientation or sexual behavior; sexual identity is not necessarily the same as one sexual orientation or sexual behavior, due to various reasons, such as the fear of identifying their sexual orientation in a homophobic setting. Reality pornography is professionally made porn which seeks to emulate the style of amateur pornography. Individuals are also sometimes abbreviated when referred to in writing, so a dominant person may be referred to as a Dom for a man, and a Domme for a woman. Men may also rub or massage the glans, the rim of the glans, and the frenular delta.