Key word mining

Exact match will only show for search results where the user searched specifically
for your keyword phrase, and only your keyword phrase.

Phrase match will show when your exact phrase appears anywhere within the
search query with the words in the same order.

Google and Yahoo! may show broad match ads when people search for synonyms
of your keywords, or if your keywords appear in the search in any order your ads
will display.

If you are new to pay per click you may want to use exact match until you get a feel
for pay per click advertising, unless you are using broad match for keyword mining.