The Oxford English Dictionary ("the definitive record of the English language"
gives these definitions related to theater:
Flop: "A person or enterprise (esp. a play, etc.) that is a failure."
Hit: "A successful stroke made in action or performance of any kind; esp. any popular success (a person, a play, a song, etc.) in public entertainment."
Obviously, folks have different opinions about whether profitability, awards, critical acclaim, or popularity are the most salient criteria of failure or success. Among the options, winning a Tony and triggering recoupment clauses by reaching profit are objective, so probably easiest to agree upon. Critical acclaim and popularity may be more subjective, but arguably valid options. When the criterion is in doubt, a speaker can always clarify which one he or she is using.