Professional Manhattan theatres not located on Broadway's famous " Great White Way". Generally, Off-Broadway productions are smaller in scale and tend to be more experimental, although Off-Broadway shows that turn into big hits are often "transferred" to Broadway itself.
The New York professional theatre located outside the Broadway district; principally in Greenwich Village and around the upper East and West Sides. Developed in the 1950s, when it was considered highly experimental, the off-Broadway theatre is now more of a scaled-down version of the Broadway theatre, featuring musicals and commercial revivals as much as (or more than) original works.
Typically, the home of noncommercial (and historically nonprofit) theatre. Tends to be much more serious and arty than Broadway. Unexpectedly popular offerings, like Hair, sometimes find their way to Broadway "legitimacy." Assassins, on the other hand, which ran for two months off-Broadway, was the usual Sondheim flop that has since attracted a devoted following. Urinetown moved from off-Broadway to Broadway status with almost its entire cast intact and has become a hit. The Golden Apple did the same thing and tanked.
Off-Broadway plays or musicals are performed in New York City in smaller theatres than Broadway, but larger than Off-Off-Broadway, productions.