Full Idea
Impredicative Definitions are definitions of an object by reference to the totality to which the object itself (and perhaps also things definable only in terms of that object) belong.
Gist of Idea
Impredicative Definitions refer to the totality to which the object itself belongs
Source
Kurt Gödel (Russell's Mathematical Logic [1944], n 13)
Book Reference
'Philosophy of Mathematics: readings (2nd)', ed/tr. Benacerraf/Putnam [CUP 1983], p.455