The term appeared occasionally in print until the 1980s and then in context to the AIDS epidemic and the discussion of sexual practices. The term was included in the 1972 publication, Playboy's Book of Forbidden Words: A Liberated Dictionary of Improper English. The term was used by G.I.s during the Vietnam War when sex without the use of a condom was known as 'going in' or 'riding' bareback. It is not known when the term (as sexual slang) was first used, although its use did gain momentum in the 1960s with the first appearance in print (as analogous reference) occurring in 1968. A slang term, bareback sex comes from the equestrian term bareback, which refers to the practice of riding a horse without a saddle.