The clear fluid that a man's penis discharges, when first sexually aroused, prior to orgasm and ejaculation of semen.
This is the fluid secreted prior to orgasm, or prior to the discharge of the actual semen.
Usually it is lighter in color than semen.
As well, pre cum is usually thinner in its viscosity than semen, aiding in its secondary purpose as a lubricant.
During a state of arousal, the male's penis can secrete a generally clear fluid, or lighter in color fluid, that contains various chemicals including sperm.
Not all men will create this fluid, while others may discharge as much as 5ml.
The fluid itself, acts as a cleansing agent for the urethra tube, which can be acidic. This fluid generally neutralizes the residual urine inside, which can harm the sperm, as it passes through.
This cleansing is help promote the survival of the sperm, for impregnation.
There are some semen markers that are NOT present in pre cum while there are some chemicals found in both semen, and pre cum.
Practice (Associated Acts): Pre Cum is a natural lubricant, that helps in the repeated penetration of the penis into the vagina, or anus.
It also helps as a lubricant during masturbation, though it may not be of sufficient duration, or such, requiring external lubrication products to help in the process.
Noteworthy: In the Muslim faith, (Sunni Islam) the presence of pre ejaculatory fluid can be a sign that the person may require a ritualistic purification ceremony.
Most other religions seem to have no opinion on pre cum, though some have some strong opinion on ejaculation, other than for impregnating a woman.
Actual 'cum' has about 6 calories of nutritional value, for an average sized load. No value has been determined for pre cum.
Pre Cum is also considered a major cause of unwanted teenage pregnancies, as most assume it has no survivable sperm and do not complete sexual intercourse. It also is due to lack of a condom or other birth control practices.
However no major studies have shown any presence of sperm in pre ejaculatory fluid. In fact smaller studies have concluded that sperm does not exist in initial pre cum.
Though it is believed that sperm can remain as a residue from an earlier ejaculation.
Some studies have clearly shown that the HIV virus, that leads to AIDs, can be present in pre cum. This puts the concept of simply penetrating one's partner but not ejaculating as being just as unsafe, as ejaculating within the person, without a condom.
Just as the Urethra can be acidic, the woman's vagina is as well, and the presence of this pre semen fluid helps to neutralize that acidity, to again, promote the survival of the sperm in its passage between bodies.
The fluid acts like a barrier or neutralizing agent.