Impossible means that something cannot happen or cannot be done, no matter how hard you try or how much you want it. If your teacher asks you to count to infinity by tomorrow morning, that's impossible because infinity never ends. If someone claims they can turn lead into gold with magic words, that's impossible because the laws of physics don't work that way.

Sometimes people use “impossible” loosely to mean “extremely difficult.” A challenging math problem might feel impossible at first, but with enough time and effort, you might solve it. When something is truly impossible, though, no amount of effort will make it happen: you can't be in two places at once, you can't unscramble an egg, and you can't travel backward in time.

When people accomplish something that seemed impossible, we often say they did the impossible, but what we really mean is that they did something extraordinarily difficult that most people thought couldn't be done. Many things once considered impossible, like human flight or going to the moon, turned out to be merely very, very hard. True impossibilities, like making 2+2 equal 5 or creating a square circle, remain impossible.