Precum (Pre-ejaculate) is the clear, colorless, viscous fluid that emits from the urethra of a man's penis when he is sexually aroused. Well I guess, my body can't lie ;)
Precum is believed to function as a lubricant and an acid neutralizer. The amount of pre-ejaculate emitted varies widely between individual men. There are some cases where men do not pre-ejaculate and some case like mine that seems to be awfully too much. I would say it is in relationship of how turn on I am, the more turn on, the more precum the body can produce.