Here it is from Stanford Encyclopedia of Philosophy

“The groundwork for institutional definitions was laid by Arthur Danto, better known to non-philosophers as the long-time influential art critic for theNation. Danto coined the term “artworld”, by which he meant “an atmosphere of art theory.” Danto’s definition has been glossed as follows: something is a work of art if and only if (i) it has a subject (ii) about which it projects some attitude or point of view (has a style) (iii) by means of rhetorical ellipsis (usually metaphorical) which ellipsis engages audience participation in filling in what is missing, and (iv) where the work in question and the interpretations thereof require an art historical context (Danto, Carroll). Clause (iv) is what makes the definition institutionalist. The view has been criticized for entailing that art criticism written in a highly rhetorical style is art, lacking but requiring an independent account of what makes a contextart historical, and for not applying to music.”

It helped me to revisit this so I know what he is talking about when he uses the term. Enjoy!