You can use match types to control which search terms will trigger your ad. Different match types allow different levels of targeting, for example whether you want your ad to be triggered only by your exact keyword, or whether you want it to be triggered by synonyms and variations as well. There is normally a negative match type option, so you can specify if you don't want your ad to be triggered by a particular keyword. Match types vary by search engine, which means that each search engine will have their own, different targeting options.
