A "fudge word," used to describe the action or inaction of a man who is as a man deemed to be the responsble party, to mean an inappropriately close communication or socialization between a man and a woman.
"Socializing," which is a positive word can be flexibly described neutrally and romantically as "flirting," or negatively as "hitting on."
Can also mean "hitting," thus further demonstrating the flexibile nature of its meaning.
"He was hitting on his wife." Means "he was beating his wife."