Tilting is defined as an emotional state that draws away a player from optimal strategy. Originally taken from pinball machines where the moving of the game (which you'd do when angry that a ball was going out) would result in the flippers being frozen and you definitely losing the ball. In those terms it's taken a situation which could be bad, to confirming it as the worst situation. You can see how that would have parrallels with poker, but it's also true of sports and casino betting.
Leave emotion at the door at the door is the mantra, and as I've mentioned before regarding matched betting, in it's simplest terms if you care about the result then you're doing it wrong. That is true to an extent, but there are other factors at play in matched betting, not least your own time and the worth of it so it's not always so black and white.
What is for sure is that gambling can be addictive, and that there are certain things you should never do when you're in control of your money and an internet connection.
Don't bet while drunk
Don't bet when you're feeling emotionaly strained
Don't bet when you're not sure what else to do
All of these things can put you on tilt, and that's a recipe for more losses. Even a single afternoon or evening of tilting has the potential to wipe out days, weeks or even months of hard work and hard won money.
Best thing to do if you're feeling like you've lost of are losing control is to go and have a walk. The fresh air and exorcise will have a powerful affect on your mind and it should help you think clearer and get back in control. The worst thing you can do is carry on betting, so don't.
I'm fortunate enough to have never really gone on tilt in a costly way, but I know other people have and it's cost them dear. If you have an addictive personality, this might not be the game for you.