Humidity is a word you'll hear if you watch a weather report, and it's also something people love to complain about. When it's hot and there's a lot of humidity, people sweat a lot — it's uncomfortable, sticky, and your hair is likely to frizz. When the humidity gets really high, there's going to be some rain or snow. In some parts of the country, people have a saying about yucky summer weather: "It's not the heat — it's the humidity."