A condom (/ˈkɒndəm/ or UK /ˈkɒndɒm/) is a sheath-shaped barrier device that may be used during sexual intercourse to reduce the probability of pregnancy and spreading sexually transmitted infections (STIs/STDs) such as HIV/AIDS. It is rolled onto an erect penis before intercourse and physically blocks ejaculated semen from entering the body of a sexual partner. Condoms are also used during fellatio and for collection of semen for use in infertility treatment.