Negative Keywords are used to suppress ad impressions for undesirable keywords.
They are extremely valuable as they ensure your ad doesn’t show for something you don’t offer, like "free".
Using them causes your CTR (clickthrough rate) to rise, giving you better relevancy and Quality Score, and the possibility to pay less for your clicks (hence buy more [...]

Ad Impressions are the number of times your AdWords Ad was displayed on someone’s computer screen, having typed the same keyword into their browser you were bidding on in your keyword list.
Since there are many pages of search results and ads, just because your Ad received Impressions, doesn’t mean it was *actually read*.
If your AdRank [...]