Other forms: stadiums; stadia
A stadium is a large outdoor venue for sports or concerts. If you were a Roman emperor, you might've watched a chariot race at a stadium, but these days you're more likely to go to a stadium to see a football game or your favorite band.
The word stadium is the Latin form of the Greek stadion, which was a length of about 600 human feet. Running tracks at the earliest Greek Olympics were approximately one stadion in length, and Roman tracks of a similar size were surrounded by tiered seating — which led to the English meaning of stadium, a track or field in the middle of tiered seats.