The term Sexual revolution was coined by Wilhelm Reich in his book The Sexual Revolution. That book was first published in 1936 in German, translated into English. The English edition was 1945.
Reich wrote in the book what he saw as wrong, namely the double standard regarding morals in the society of his time. These double standards and the suppression of the sex drive would make people different. This would lead to a buildup of aggressions and frustration. Freeing the sex drive would lead to a peaceful change of society, according to Reich.
Reich dies in prison 1957, but his ideas had their effect in the 1960s when people changed their views about sex. They were more open-minded about it. The publications of people like Alfred Kinsey helped give wings to the movement.