Erwin Schrödinger and his cat's thought experiment is about locking a cat in an opaque box with atomic manure. Since nobody really knows whether the cat is still alive or when it is dead, one can assume that it is both alive and dead - to put it simply. The Wikipedia puts it a little more complicated:
The paradox is that, according to the thought experiment, a cat could be brought into a state in which it is "alive" and "dead" at the same time using the rules of quantum mechanics, and remains in this state until the experimental set-up is examined. The cat, dead and alive at the same time, would only be clearly defined as “alive” or “dead” if it was observed, i.e. a measurement was carried out. This contradicts the view and everyday experience with macroscopic systems.
Exciting and yet a bit absurd - but not as absurd as the following animated film by Chavdar Yordanovthat he did for an animation show in London. It doesn't provide a much simpler explanation of the experiment, but I like the style of animation and if it has to be crazy, then please do it right! And what do we learn from this? You don't experiment with cats!