What does "make eyes at" mean?

Ogle, flirt with, as in To her sister's disgust, she was always making eyes at the boys. Although slightly different versions, such as throw the eye at, are much older, this precise locution was first recorded in William Makepeace Thackeray's Henry Esmond (1852): “She used to make eyes at the Duke of Marlborough.” See also give someone the once-over.