A condom is a barrier device, typically a thin sheath (male/external or female/internal), used for contraception to prevent pregnancy and protect against sexually transmitted infections (STIs) like HIV, by preventing sperm and infections from entering the body during sex. Made from latex, polyurethane, or polyisoprene, they come in various types (thin, dotted, ribbed, flavored) and must be used correctly and consistently with each sexual encounter for maximum effectiveness, using only water-based or silicone-based lubricants.