The Collaborative International Dictionary of English v.0.48:

Apple pie \Ap"ple pie`\
   A pie made of apples (usually sliced or stewed) with spice
   and sugar.
   [1913 Webster]

   Apple-pie bed, a bed in which, as a joke, the sheets are so
      doubled (like the cover of an apple turnover) as to
      prevent any one from getting at his length between them.
      --Halliwell --Conybeare.

   Apple-pie order, perfect order or arrangement. [Colloq.]
      --Halliwell.
      [1913 Webster]

WordNet (r) 3.0 (2006):

apple pie
    n 1: pie (with a top crust) containing sliced apples and sugar