The Collaborative International Dictionary of English v.0.48:

Albacore \Al"ba*core\, n. (Zool.)
   A name applied to several large fishes of the Mackerel family
   (Scombridae), esp. Thunnus alalunga (formerly Orcynus
   alalonga); it is a type of tuna or tunny. The name has been
   also applied to a larger related species, Thunnus thynnus
   (formerly Orcynus thynnus), common in the Mediterranean and
   Atlantic, which is called in New England the horse
   mackerel. [formerly spelled albicore.]
   [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

albacore
    n 1: relatively small tuna with choice white flesh; major source
         of canned tuna
    2: large pelagic tuna the source of most canned tuna; reaches 93
       pounds and has long pectoral fins; found worldwide in
       tropical and temperate waters [syn: albacore, long-fin
       tunny, Thunnus alalunga]