Sentence:  User calls <code>RouteCollection.GetVirtualPath</code>, passing in a <code>RequestContext</code>, a <WSD>dictionary</WSD> of values, and an optional route name used to select the correct route to generate the URL. 
Meaning of the word marked with <WSD> tags:  An associative array, a data structure where each value is referenced by a particular key, analogous to words and definitions in a physical dictionary.