The Collaborative International Dictionary of English v.0.48:

Balkans \Balkans\ prop. n. pl.
   1. The countries occupying the Balkan Peninsula.

   Syn: Balkan countries, Balkan nations, Balkan states.
        [WordNet 1.5]

   2. The Balkan mountains.
      [PJC]

WordNet (r) 3.0 (2006):

Balkans
    n 1: the major mountain range of Bulgaria and the Balkan
         Peninsula [syn: Balkans, Balkan Mountains, Balkan
         Mountain Range]
    2: a large peninsula in southeastern Europe containing the
       Balkan Mountain Range [syn: Balkan Peninsula, Balkans]
    3: the Balkan countries collectively