What it means
Google rewards relevance. Quality Score blends expected click-through rate, ad relevance, and landing-page experience. The better the match between what someone searched, the ad they see, and the page they land on, the less you pay for the same position.
Why it matters
Two advertisers can bid the same and pay very different prices. Improving Quality Score is one of the few ways to cut CPC without cutting reach — tighten ad groups, mirror the query in the ad, and make the landing page deliver on the promise.