STD stands for Sexually Transmitted Disease. (This is something you may already know.) STI, less familiar than the term STD, stands for Sexually Transmitted Infection. What's the difference?

For the purpose of this discussion, STD are viral (and at the moment, incurable, though treatable). STDs include: HIV, herpes, and . Hepatitis is also a virus that can be transmitted sexually. (Vaccines are available for hepatitis A and B, though not C. Some people who catch Hep A or B get through the infection and then get over it, while others remain infectious. There is a low success rate for treatments of Hep C.)

For the purposes of this discussion, STI are bacterial or parasitic, and can be cured with appropriate treatment. THese would include: chlamydia, gonorrhea, syphilis, trichomoniasis, scabies, and pubic lice. Also, yeast infections, while not really considered an STI, can be passed back and forth between partners is proper steps are not taken.

All in all, none of these are terribly fun or desirable.