There comes a few drops of lubricating fluid from the man's penis when he is excited. This pre-ejaculate is humoristically called "speed drop".
This happens at an early stage during sex, long before the man gets his orgasm (with actual ejaculation of sperm).
The problem is that the pre-ejaculate may include some sperm cells, which can make the woman pregnant! That's why the with-drawal method (
coitus interruptus) is not a very safe way to avoid pregnancy.