Most of the time, when you want to improve your website's search engine rankings, you add content. Maybe you want to target a new keyword, so you write a blog post based on it. Perhaps you want to improve a page's ranking, so you add a video or some search engine optimization (SEO)-friendly copy to it.
While adding content is often an appropriate approach, removing website content can also improve your rankings under the right circumstances. This optimization tactic is called content pruning SEO.