From W3C Wiki
The web closure of an RDF graph is the graph you get if you merge the results of performing web retrieval on all the URIs in the graph (following redirects as needed), recursively, until they have all been followed.
The full WebClosure of many graphs will be impractically large, but there may be techniques for finding interesting subgraphs of the closure.
This is motivated by the desire to FollowLinksForMoreInformation.
One restricted kinds of WebClosure are the OntologicalClosure, DefinitionalWebClosure, and is DocRulesClosure.