With the new Priority Search, you tell Ancestry.com which national or ethnic records are most relevant to your search. When you select a specific nationality or ethnicity, the Ancestry.com search engine will give databases with data pertinent to that nationality or ethnicity more weight when search results are returned.
In addition, choosing to prioritize a search helps Ancestry.com know which Soundex algorithm and/or name dictionaries to use to better approximate matches for the names you’re searching.
Look for the “Give priority to” drop-down menu on Ancestry.com search screens.
Anne Mitchell, search product manager, discusses Priority Search on the Ancestry blog: http://blogs.ancestry.com/ancestry/2008/10/28/focusing-your-search-with-the-collections-options/