Source : Webster's Revised Unabridged Dictionary (1913)

Whey \Whey\, n. [AS. hw[ae]g; cf. D. wei, hui, Fries. weye, LG.
   wey, waje. ]
   The serum, or watery part, of milk, separated from the more
   thick or coagulable part, esp. in the process of making
   cheese.

   Note: In this process, the thick part is called {curd}, and
         the thin part whey.

Source : WordNet®

whey
     n 1: the serum or watery part of milk that is separated from the
          curd in making cheese [syn: {milk whey}]
     2: watery part of milk produced when raw milk sours and
        coagulates; "Little Miss Muffet sat on a tuffet eating
        some curds and whey"