STD stands for Sexually Transmitted Disease. These diseases are sometimes known as Sexually Transmitted Infections (STIs). An STI is any infection that is passed by body fluids during vaginal, anal or oral sex. These fluids include semen (cum), vaginal fluids (the wetness in the vagina) and blood. A latex condom acts as a barrier to prevent these fluids from being exchanged. But, an STI can also be spread by contact with the skin of the genital or anal area if infection is present. It can also be spread by contact inside of the mouth.
Some common STIs are HIV infection (AIDS), syphilis, gonorrhea, chlamydia, trichomoniasis, human papillomavirus infection (HPV), genital herpes and hepatitis B. While most STIs can be treated, many cannot be cured. They stay with you for your whole life.