Search algorithms are what (say) Google requires for its ranking systems to be able to sift through hundreds of billions of webpages in its entire search index to find the most relevant
results, all within a fraction of a second, to present them in a way that helps us searchers find what we’re looking for. Search algorithms look at many factors, including the words within a query, the relevance and usability of pages, expertise of sources and the searcher’s location and settings (this can blend with Google My Business).
To help ensure that Search algorithms meet high standards of relevance and quality, Google has a process
that involves live tests and trained external international Search Quality Raters, who follow strict guidelines