Undisputed means accepted by everyone as true or real, with no one disagreeing or challenging it. When something is undisputed, there's no argument about it.

If someone is the undisputed champion of a sport, everyone agrees they're the best. There's no other person who can claim the title or say “actually, I won too.” When a boxer holds the undisputed heavyweight championship, he's won all the major championship belts, so there's simply no debate about who's on top.

You might hear that George Washington was an important leader of the American Revolution, or that a particular student is the undisputed spelling bee champion of her school. These statements mean no reasonable person would disagree.

Sometimes people use the phrase “undisputed fact” to emphasize that something is absolutely, definitely true: it's an undisputed fact that the Earth orbits the Sun, or that water freezes at 32 degrees Fahrenheit (0 degrees Celsius). When something is undisputed, the discussion is over because everyone's on the same page.