AdWords gives you the ability to decide how precise a user's search phrase must be to trigger your ad on Google search pages. You have the following options:
Your ad will get triggered for any variation of your keyword or phrase in a search query. This option reaches the most users. For example, if your keyword is San Jose Sharks then San Jose White Sharks will also trigger your ad.
This option narrows your reach by showing your ad only when the search term contains your keyword. You can set this preference by including your keyword in double quotations. For example, if your phrase match is "San Jose Sharks," then your ad will not be triggered for search queries like the San Jose White Sharks. However, your ad can be displayed for search terms like San Jose Sharks Museums.
This option further narrows your reach by only showing your ad when the search term is exactly the same as your keyword. You can set this preference by including square brackets around your keyword. For example, [San Jose Sharks] will now trigger an ad only when the search query matches the entire phrase as it is.
Negative keywords are filtering keywords. Negative match type prevents your ad from showing when a word or phrase you specify is part of a search term. You can set this option by putting a minus sign before your keyword. For example -"great white". -"white sharks", -"shark museums", -"aquarium".