expression, godan verb (-ru)
cast amorous glances; make eyes at; give the eye
Idiomatic expression used when a woman sends flirtatious looks to a man. Often carries a literary or slightly old-fashioned tone.
彼女はパーティーで彼に秋波を送っていた。
She was making eyes at him at the party.
More casual and direct; can be used for both men and women, while 秋波を送る is specifically about a woman's glance and has a literary feel.
From Chinese classical literature, where 秋波 (autumn ripples) metaphorically describes the clear, attractive eyes of a beautiful woman. The phrase entered Japanese as a set expression.