STDs are sexually transmitted diseases. This means they are most often -- but not exclusively -- spread by sexual intercourse. HIV, chlamydia, genital herpes, genital warts, gonorrhea, some forms of hepatitis, syphilis, and trichomoniasis are STDs.STDs used to be called venereal diseases or VD.They are among the most common contagious diseases. More than 65 million Americans have an incurable STD. Each year, 20 million new cases are reported; half of these infections are among people ages 15 to 24 and they can have long-term consequences.TDs used to be called venereal diseases or VD. They are among the most common contagious diseases. More than 65 million Americans have an incurable STD. Each year, 20 million new cases are reported; half of these infections are among people ages 15 to 24 and they can have long-term consequences.