All major search engines (Google, Bing and Yahoo) filter in order to provide searchers with higher-quality and more relevant results. There are, however, a number of smaller search engines that specifically advertise that they don’t filter results before ranking them for the searcher.
There has been quite a bit of buzz about a “filter bubble,” or concern over the way in which results limited by filters may reinforce certain beliefs and restrict the incursion of new ideas. Search personalization, people concerned about the filter bubble say, perpetuates ignorance by showing users only what they want to see.
Certain qualities of webpages can cause search engines to filter—or simply remove—them from search results. These include black-hat SEO techniques and bad practices like keyword stuffing, duplicating content, hiding text so that it remains searchable but hidden, using too many internal links, paying for any links or paying for traffic.
Users can also manually filter their search results, typically using options provided at the top of the page. On the major search engines, these include category filters (photos, videos, news, maps, etc.). Within these categories, one can choose to see only results posted within the last 24 hours, photos of specific colors or sizes, and so forth.