Personalization is a term used that Google uses to bring the correct SERPs (search engine results pages) to a person that is doing a search in their search engine. The results of the SERPs depend upon the person’s location, browser history, search history, what ads they clicked on before, etc. This is all taken into determination to show the proper websites when they do a search online.

For example, if a person frequently visits railroad websites and visits railroad forums when they do a search for “images of tracks” they will more than likely get images of railroad tracks instead of car racing tracks.