What's the difference between Broadway and Off-Broadway? One seat ... literally.
With a good dose of money invested, an Off-Broadway production can be as glitzy and fabulous as anything on the Great White Way. But the actual determination of what constitutes a Broadway house -- and ergo, a Broadway show -- is the number of seats in the theatre.
A Broadway house has 500 seats whereas an Off-Broadway theatre has 100 to 499 seats. Off-Off Broadway theatres only have 99 seats ... or fewer.
Bonus Points: Currently, 38 theatres are recognized as Broadway houses in New York City.