If you have a Google account and use the Google search while logged in, the search engine will try to improve your results by relying on keywords you searched for before and on the websites you visited. In the official help file, they describe this personalized search as follows:

When you search using Google, you get more relevant, useful search results, recommendations, and other personalized features. By personalizing your results, we hope to deliver you the most useful, relevant information on the Internet.

If you use personalized search and have the new beta search interface enabled (enable the new Google Search Interface), Google will show this message on the bottom of each search results page: