To understate something means to describe it as less important, impressive, or extreme than it really is. When you understate, you minimize or downplay the truth.

If someone asks how your basketball game went and your team won 85 to 30, saying “we did okay” would be understating your victory. You're not lying, but you're presenting the truth in a way that makes it seem smaller than it actually was. When a scientist discovers something revolutionary and says “these findings might be somewhat interesting,” she's understating the significance of her work.

Sometimes people understate things on purpose, perhaps out of modesty or to avoid seeming boastful. Other times they might understate a problem because they don't want to face how serious it is. Saying “I'm a little behind on my homework” when you haven't done any assignments for two weeks would be quite an understatement.

The opposite is overstate, which means to make something sound bigger or more important than it truly is. An understatement (the noun form) is often used for humorous effect, like calling a blizzard “a bit of snow” or describing a massive feast as “a light snack.”