Pre-ejaculate (a.k.a. pre-cum) is a clear fluid that comes out of a guy's penis when he becomes erect. Pre-cum usually appears before a male reaches orgasm, which can happen during masturbation, foreplay or the early stages of sex. Since pre-cum carries very little sperm, it's unlikely that a pregnancy will occur from this sexual fluid, but it is still a possibility. Pre-ejaculate can also cause the spread of STDs, including HIV.
Semen, also known as ejaculate, is the fluid created by the testes. When semen goes into the vagina during sex, it can possibly lead to pregnancy or sexually transmitted diseases.
