XXX on broad match encompasses thousands of other "related" search terms. For instance if you bid on XXX on broad match, it may also show your ads for searches for "porn," "sex," etc., based on your websites content; withOUT having "XXX" in the query.
However on phrase match, your ads will ONLY show if "XXX" appears in the search query.
Broad match keywords = bad idea unless you REALLY know what your doing and have a strong negative keyword list
