An opinion is a judgment, viewpoint, or statement that is not conclusive, rather than facts, which are true statements.
"Soapboxing" in Chinatown, San Francisco
A fact is a true datum about one or more aspects of a circumstance. Standard reference works are often used to check facts. Scientific facts are verified by repeatable careful observation or measurement by experiments or other means.
Non-fiction books at a Danish library, shelves displaying the word Fakta, Danish for "Facts"