Full Idea
Vagueness in a concept is its indiscriminability from other possible concepts; this can be reconciled with our knowledge of vague terms.
Gist of Idea
Vagueness in a concept is its indiscriminability from other possible concepts
Source
Timothy Williamson (Vagueness [1994], 8.1)
Book Reference
Williamson,Timothy: 'Vagueness' [Routledge 1996], p.217
A Reaction
Sorensen objects that this makes vagueness too relative to members of a speech community. He prefers 'absolute borderline cases'. If you like the epistemic view, then Williamson seems more plausible. My 'vague' might differ from yours.