Improbability is the quality of being unlikely to happen. When something has a high degree of improbability, the odds are stacked against it occurring.

If you shuffled a deck of cards and dealt yourself a perfect hand of all thirteen spades in order from ace to king, you'd witness an event of stunning improbability. It's possible, but the chances are so tiny that you could shuffle cards your entire life and never see it happen. That's what improbability means: something could theoretically occur, but probably won't.

Scientists and mathematicians often measure improbability using percentages or ratios. A weather forecaster might say there's a 5% chance of snow in July, describing an event of high improbability. The improbability of winning the lottery doesn't stop millions from playing, even though winning is extremely unlikely.

Notice that improbability isn't the same as impossibility. It's not impossible to flip a coin and get heads twenty times in a row, but the improbability is enormous. Understanding improbability helps you think clearly about risk, luck, and what's actually likely to happen, versus what merely could happen.