A conom is a device most commonly used during sexual intercourse. It is put on a man's erect penis and physically blocks ejaculated semen from entering the body of a sexual partner. Condoms are used to prevent pregnancy and transmission of sexually transmitted diseases (STDs—such as gonorrhea, syphilis, and HIV). Because condoms are waterproof, elastic, and durable, they are also used in a variety of secondary applications. These range from creating waterproof microphones to protecting rifle barrels from clogging.