An STI is sometimes referred to as a sexually transmitted disease (STD) or venereal disease (VD). A sexually transmitted infection (STI) is an infection that can be passed from person to person when having sex. You can get an STI by having vaginal sex, anal sex, or oral sex. There are several different types of STI. Before becoming sexually active with a new partner or if you have had recent multiple partners is an opportune time to consider STI screening.