What is impossible?

There is a fun picture post below. i like picture posts more, its fantastic fun to look at all the results you get for random thoughts. It really is. The story behind the pictures is often times more intriguing then the actual pictures themselves. Check it out for yourself sometime.
I have been thinking today. A rare event I know :P.
What is impossible?? Is it really a thing, or is it just a word. A word that has no definition, a meaning that is not there unless we put it there. Impossible does not exist in nature. Animals don't know the meaning of impossible, nothing is impossible to them, because they have not created a world of impossible. I ask myself... "Is impossible something that really exists, or have we given it existence?? Have we birthed the very thing that we try to go out and defeat then?? Is impossible just another way of saying impropable, or is it a real thing??"
People might say that somethings are impossible. After all, a human can't fly on their own, we don't have wings. Humans can't outrun a cheetah, we don't have the speed. But people once thought we would never run a mile in under 4 minutes. Now the world record is 3 minutes and 43 seconds. People once gazed at the moon in wonderment, now we have had a man walk on that very same moon. We know the depths of the ocean, the genetic code that makes us human and even have found ways to break every record man has ever had. Is impossible really impossible?? Or do we just make obstacles impossible, almost as if it would take a gargantuan effort from a hero who is larger then life to break the barrier. I would venture to say we do. We need something to inspire us to achieve limits we previously thought "impossible". And then once we do break those walls down, pass the unpassable, beat the unbeatable, we admire the accomplishment as being inhuman, that is until another repeats the feat, and another, and another, until eventually it is regarded as just another part of everyday life. To think we could create weapons that would be capable of destroying our entire world. Thats amazing considering just 500 years ago swords were still the best weapon available to a man. Amazing.
Impossible is nothing and nothing is impossible... Right....