You may have heard the phrase "Schrödinger's cat," but like me, you may not have entirely understood what it meant. But I get it now, having watched the video below. It's from scientists at the University of Nottingham in England, and in their Sixty Symbols project (a companion to the Periodic Table of Videos) they are producing videos explaining various symbols used in physics and astronomy. Schrödinger's cat isn't a symbol in the traditional sense, such as the Greek letters that often pop up in physics equations, but it definitely could benefit from some explanation.
Austrian physicist Erwin Schrödinger used the cat in a thought experiment to demonstrate that it was ridiculous to apply a feature of quantum mechanics to everyday objects like a cat. That feature is that an object can be in two different states simultaneously. And while this may be possible at the quantum mechanical level, it is not with a cat, for example, which cannot be both dead and alive.