三陪 emerged in 1990s China as a euphemism for hostess work in karaoke bars and nightclubs. The "three" refers to
陪酒 (drinking with),
陪舞 (dancing with), and
陪唱 (singing with) male customers — often a thin cover for prostitution (sometimes called
四陪 when
陪睡 "sleeping with" is added). The common collocation is
三陪小姐 (sānpéi xiǎojiě). It's police-blotter and tabloid vocabulary, not for polite conversation.