Google AdWords Keyword-Matching Options
Google can match your ads with users' searches in more than one way, giving you a better chance of connecting with exactly the customers you're looking for.
Broad match: Plain keywords are matched broadly to related words at Google's discretion. Broad matching saves you from having to think of related keywords but can lower an ad's performance by showing it on pages less likely to deliver clickthroughs.
Negative match: Used effectively with broadly matched keywords, negative matches exclude words from triggering your ads.
Phrase match: Enclosing a key phrase in quotation marks makes Google match it exactly when triggering ads, but Google also broad-matches the phrase with other words and phrases. Phrase matching is good when you want broad distribution focused around an explicit phrase.
Exact phrase: Enclosing a key phrase in brackets forces Google to match the phrase exactly when triggering your ads and excludes any other words from matching.