An STD is a medical condition that is spread through sexual contact. Sometimes, sexually transmitted diseases are referred to as sexually transmitted infections or STIs. There are a number of STIs that can be transmitted through oral, vaginal or anal intercourse. Common STIs include genital herpes, human papillomavirus (HPV), chlamydia, gonorrhea, syphilis, and hepatitis C. You can help reduce your risk of contracting an STD by using condoms during sex.