AdWords attempts match your keywords with searches in Google and occasionally (sometimes often actually!) your ads will appear for search terms you really don’t want.
The dilemma is that you don’t readily get to see those mismatches and could easily assume that everything is OK fine, so checking your Search Term Report regularly is a key maintenance activity.

Login and go to a keyword view; Click the Dimensions tab and use the View dropdown (extreme left) and scroll down and select Search Terms
You will discover a whole new world of search terms which typically differ markedly from your configured keywords

This is where Keyword Matching comes into play:

Broad match indicates AdWords will match anything similar to your keywords in any order

Modified broad match AdWords will match the modified term (or close variations, but not synonyms), in any order

Phrase match  AdWords will match a search includes your keywords plus additional terms

Exact match  indicates AdWords will only match your exact keywords

Negative match AdWords will not match searches if they contain your negative keyword

This is described and illustrated here with examples of how it works

Setting up Keyword Matching can be complex, so reviewing your Search Term Report is a useful way of determining if you are getting the results you want

Posted in: AdWords