Encyclopedia Britannica defines it as a "computer program to find answers to queries in a collection of information, which might be a library catalog or a database but is most commonly the World Wide Web."
The Britannica article goes on to say that search engines rank results using different techniques. None of these techniques can guarantee that you're getting reliable information. In addition, no search engine can actively keep up with every web page that is published on the web.
That said, there are a lot of good search engines out there for different purposes, and Google is just one.
This article from RankRED discusses some alternatives, including:
WolframAlpha - A knowledge search engine that can answer factual questions.
DuckDuckGo - Doesn't track your data. Blocks trackers that sell your information to advertisers.
Some search engines keep track of your search history. If your results are different from your friends', then this is probably why. If you're concerned about that, try a search engine that will protect your privacy.
Some search engines also rank paid results first, so if you are tired of seeing ads, you can try a search engine that's open source or is run by a non-profit.