“Basically, it refers to whether or not a belief can be proven wrong. If I tell you that I weigh 70 pounds, this is a claim that can be easily tested and promptly thrown out by bringing me to a scale — that is, it’s falsifiable. If, on the other hand, I tell you that everything in the universe is controlled by an invisible astral monkey with a million arms, then there’s little you can do to prove, empirically, that this is a zany notion.”