Wiktionary
intercrural sex
n. A non-penetrative form of sex in which a man's penis is stimulated between his partner's thighs.
Wikipedia
Intercrural sex
Intercrural sex (from inter- and Latin crura, "legs"), also known as femoral/interfemoral sex/intercourse, is a type of non-penetrative sex, in which a male places the penis between the receiving partner's thighs (often with lubrication), and thrusts to create friction.