At what point is it considered cheating?

So a friend and I were having a discussion about cheating and we couldn't fully agree on what is the definition of a cheater. Obviously intercourse is cheating but what else would you consider cheating? Exchanging numbers without the intent to actually call? Is it the messages that flow back and forth between two individuals without their significant other knowing? Is having wandering eyes considered cheating? Compliments or being flirtatious? Comment below with your opinion.