heads up (Adjective) — Fully alert and watchful. ex. "played heads-up ball"
heads up (Noun) — An advisory notice; a call to pay attention to or look at something. ex. "thanks for the heads up about the new edition"
heads up (Noun) — A warning message. ex. "he sent a heads-up to the District Attorney"
heads up (Verb) — Be the first or leading member of (a group) and excel. ex. "This student heads up the class"