wanton girl; promiscuous woman
A set phrase describing a woman who is sexually loose or easily sleeps around. Often carries a derogatory or judgmental tone.
There's a rumor going around that she's a promiscuous woman.
That guy only chases after easy women.
A more general term for a person who cheats or is unfaithful, not necessarily focused on sexual looseness.
Literally 'a woman with a light buttocks'. The phrase uses 尻 (buttocks) metaphorically for sexual behavior, and 軽い (light) to imply easiness or lack of restraint.