The Collaborative International Dictionary of English v.0.48:

drive-in \drive-in\ n.
   any installation designed to accommodate patrons while
   staying in their automobiles; especially an outdoor movie
   theater in which patrons park in their vehicles to watch the
   movie.
   [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

drive-in \drive-in\ a.
   arranged to allow business to be transacted while patrons
   remain in their vehicles; as, a drive-in window at a bank.

   Syn: drive-through. [WordNet 1.5]

WordNet (r) 3.0 (2006):

drive-in
    n 1: any installation designed to accommodate patrons in their
         automobiles