Fact
An opinion is different from a fact. But you can say facts about a person's opinion. For example, someone can ask a question like "What is Alice's opinion about the book?" You can answer this question with a fact, for example "Alice said she likes the book." Then it is a fact that Alice says she likes the book. But maybe Alice does not like the book. So it is not a fact that Alice likes the book, but it is a fact that Alice says she likes the book.