noun
footjob
Slang term for a sexual act involving stimulation with the feet. Strongly vulgar; not used in polite conversation.
彼女は彼に足コキをしてあげた。
She gave him a footjob.
Compound of 足 (あし, 'foot') and コキ, from 扱く (こく, 'to rub, to pump'). The exact derivation is uncertain, but the term is modern slang.