The Collaborative International Dictionary of English v.0.48:

off-Broadway \off-Broadway\ prop. a.
   Of or pertaining to the professional theaters in Manhattan
   not in the Broadway area; performed in off-Broadway[1].
   [PJC]

The Collaborative International Dictionary of English v.0.48:

off-Broadway \off-Broadway\ prop. n.
   1. A group of low-budget theaters located outside the
      Broadway area in Manhattan.
      [WordNet 1.5]

   2. The professional drama presented in off-Broadway theaters.
      [PJC] off-center

WordNet (r) 3.0 (2006):

off-Broadway
    n 1: low-budget theaters located outside the Broadway area in
         Manhattan