'Federated search' is also known as, meta-search, cross-search, combined-search, integrated search and aggregated-search. First, it is about simultaneously searching, with one-click, in several electronic sources. Second, it is about getting all the search results displayed in a single browser.
But then, some tend to use the term, Federated search, for searching OPAC / Union Catalogs / serial holdings, see: 360 Search service and R-search; and some extend to searching Websites (not just the surface web, they attempt to reach the deep web), see: here and here -- the latter refers to an example of Dogpile, as an aggregator (see much more on meta-search in relation to Search Engines, yahoo, google, bing, etc.).
On the same shelf: