what is an sti or std
STDs/STIs. Sexually transmitted diseases, or STDs (sometimes called sexually transmitted infections, or STIs) affect people of all ages, backgrounds, and from all walks of life. In the U.S. alone there are approximately 20 million new cases each year, about half of which occur among youth ages 15-24 years.
Any STD/STI can be spread through sexual intercourse, and some STDs/STIs also are spread through oral sex and sex play. Ejaculation does not have to occur for an STD/STI to be passed from person to person.