The Collaborative International Dictionary of English v.0.48:

Leakage \Leak"age\, n. [Cf. D. lekkage, for sense 1.]
   1. A leaking; also, the quantity that enters or issues by
      leaking.
      [1913 Webster]

   2. (Com.) An allowance of a certain rate per cent for the
      leaking of casks, or waste of liquors by leaking.
      [1913 Webster]

   3. (Elec.) A leak[3]; also; the quantity of electricity
      thus wasted.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

leakage
    n 1: the discharge of a fluid from some container; "they tried
         to stop the escape of gas from the damaged pipe"; "he had
         to clean up the leak" [syn: escape, leak, leakage,
         outflow]