The Collaborative International Dictionary of English v.0.48:

middle-of-the-road \middle-of-the-road\ adj.
   1. supporting or pursuing a course of action that is neither
      liberal nor conservative.

   Syn: centrist, moderate.
        [WordNet 1.5]

   2. not extreme, especially in political views.
      [WordNet 1.5] -- middle-of-the-roader, n. --
      middle-of-the-roadism, n.

WordNet (r) 3.0 (2006):

middle-of-the-road
    adj 1: supporting or pursuing a course of action that is neither
           liberal nor conservative [syn: centrist, middle-of-
           the-road]
    2: not extreme, especially in political views