UFO – Unidentified Flying Object or more recently UAP, Unidentified Aerial Phenomena
Many stories, books, movies, reports and news articles have been produced on this subject. You need only Google these terms and you will find a large number of resources on this subject matter. Most UFO’s have been identified but many cannot be explained. As of 2022 no official source has been able to scientifically prove the existence of intelligent life on other planets.
https://www.gov.uk/government/publications/ufo-reports-in-the-uk
https://www.latimes.com/opinion/story/2021-12-16/ufos-pentagon-congress-government