The Collaborative International Dictionary of English v.0.48:

Peanut gallery \Pea"nut gal"ler*y\
   1. The cheapest seats in a theater, being typically those
      farthest from the stage, as in the uppermost balcony.
      [PJC]

   2. In a television show for children, the section where
      visiting children sit as guests during the performance.
      [PJC]

   3. Hence: Any group of children, or the chidren in a group of
      people; as, let's have no noise from the peanut gallery.
      [Colloq.]
      [PJC]

WordNet (r) 3.0 (2006):

peanut gallery
    n 1: (figurative) people whose criticisms are regarded as
         irrelevant or insignificant (resembling uneducated people
         who throw peanuts on the stage to express displeasure with
         a performance); "he ignored complaints from the peanut
         gallery"
    2: rearmost or uppermost area in the balcony containing the
       least expensive seats [syn: second balcony, family
       circle, upper balcony, peanut gallery]

Moby Thesaurus II by Grady Ward, 1.0:

43 Moby Thesaurus words for "peanut gallery":
   Texas tower, auditorium, balcony, beacon, belvedere, bleachers,
   box, box seat, bridge, conning tower, dress circle, fauteuil,
   gallery, gazebo, grandstand, lighthouse, loge, lookout, loophole,
   nigger heaven, observation post, observatory, orchestra,
   orchestra circle, outlook, overlook, paradise, parquet,
   parquet circle, parterre, peephole, pharos, pit, proscenium boxes,
   ringside, ringside seat, sighthole, stall, standing room,
   theatre stall, top gallery, tower, watchtower