and on the help page that it leads to...
Expanded Broad Match: Automatically matches your ads to words that are semantically related to the keywords on which you bid (whereas Google requires the addition of a + symbol to appear on extended broad match, adCenter does not and all keywords will be treated as extended). This match type expands on the set of queries to which an ad Broad matches. For example, if you bid on the keyword "yoga," Expanded Broad might match the ad to a search for Ashtanga, a form of yoga. Bidding on Broad match automatically counts as a bid on Expanded Broad at the same amount. Both types of Broad match appear as the Broad Match type in performance reports, if the column 'Delivered Match Type' is included.