The exchange of semen through oral, mouth, contact only
Reaching an orgasm through oral stimulation of the penis, such as lips, tongue, and throat. The actual ejaculation of one person due to the oral stimulation by another.
In Ancient Rome, giving head was considered very bad, and was a major taboo in that time. Yet in Chinese Taoism, the act of 'eating out a woman' was considered to promote long life, and was thought to be very uplifting, spiritually.
Health Risks: The exchange of any bodily fluids is considered to be risky, specially in the transmission of STD's. The presence of open wounds, sores, bleeding gums, in either the mouth or sores and wounds, on the genitals can increase the risk of such transmissions.
Diseases that can be transmitted orally, include various strains of Hepatitis, Gonorrhea, herpes, human papilloma virus (HPV), and in rare instances, HIV. Other less harmful viruses can also be transmitted through oral sex contact, such as colds and bacterial infections.
Transmission of HIV orally is considered rare, but the risks exist, and increases if one is already infected with the virus, and there are open sores or wounds in the mouth.
These risks are increased if one has just recently brushed one's teeth before or after oral sex, or digested crunchy foods such as potato chips.
Basically, this is to place one's penis between the lips (of another), to then go up and down along the shaft, until the other party reaches an orgasm, culminating by their ejaculation of semen into the mouth. The penis can be occasionally stroked by hand during the act, and the ejaculation can be on the face or mouth, though generally is done while being in the other person's mouth.
It does include, but not always, the use of the tongue in stimulating the penis, as well as inserting the penis so that a portion may actually be lodged within one's throat.
Techniques are as varied as there are willing participants. Each one has their own style, which can include excessive use of spit and other means of stimulation, including the insertion of a finger in the recipient's anus, or even the use of sexual toys (objects), or other anal stimulation techniques, while the penis is within the mouth.
Practice (Associated Acts): Auto-Fellatio is the act where no other party is involved. One is able to actually contort their own bodies, sufficiently, so that they can actually insert their own penis into their mouth, and suck on it until ejaculation. Commonly referred to as 'self sucking'.
Noteworthy: The New England Journal of Medicine (http://content.nejm.org/) reported that those who had less than five oral sex partners in their lifetime, had double the risk for Throat Cancer, while those who had more than five oral sex partners, stood a 250% increased chance of having Throat Cancer.