Full Idea
A speaker who uses a definite description 'attributively' in an assertion states something about whoever or whatever is the so-and-so; a speaker who uses it 'referentially' enables his audience to pick out whom or what he is talking about.
Gist of Idea
Definite descriptions are 'attributive' if they say something about x, and 'referential' if they pick x out
Source
Keith Donnellan (Reference and Definite Descriptions [1966], §III)
Book Reference
'Naming, Necessity, and Natural Kinds', ed/tr. Schwartz,Stephen P. [Cornell 1979], p.46
A Reaction
"Smith's murderer is insane" exemplifies the first use before he is caught, and the second use afterwards. The gist is that reference is not a purely linguistic activity, but is closer to pointing at something. This seems right.