That one basketball team that never loses a game? They're unbeatable! They can't be defeated, no matter what their opponents do.
Use this adjective for anyone who can't be beaten in a contest or game, like an unbeatable chess champion or your unbeatable show dog. Unbeatable can also be used in a more commercial way: "No one can match our unbeatable prices!" In other words, our prices are the lowest. Sometimes this adjective simply means "the best," even when there's no actual competition: "Wow, the view from your beach house is unbeatable!"