The Collaborative International Dictionary of English v.0.48:

Localism \Lo"cal*ism\, n.
   1. The state or quality of being local; affection for a
      particular place.
      [1913 Webster]

   2. A method of speaking or acting peculiar to a certain
      district; a local idiom or phrase.
      [1913 Webster]

WordNet (r) 3.0 (2006):

localism
    n 1: a phrase or pronunciation that is peculiar to a particular
         locality
    2: a partiality for some particular place [syn: sectionalism,
       provincialism, localism]