What does it mean when a guy sends mixed signals?

It means one of two things....either he is just not that into you OR he may like you but is just not sure how far he wants things to go. I know a guy like that. He told me to text him, I did, invited him out when I know neither of us have to work, and he texts me back "maybe" What the heck is that suppose to mean? Okay, Im getting the impression he's just not that into me or he's putting me on the back burner in case he gets invited somewhere else. That is so bad. I feel like sh** once again. Why do guys do that?