The correct answer is SEXUALLY TRANSMITTED INFECTION. STI stands for Sexually Transmitted Infection, which refers to infections that are primarily transmitted through sexual contact. These infections can be caused by bacteria, viruses, or parasites and can be spread through vaginal, anal, or oral sex. Common examples of STIs include chlamydia, gonorrhea, syphilis, herpes, and HIV/AIDS. It is important to practice safe sex and get regular check-ups to prevent and detect STIs early.