Facts are information that is true, not an opinion or what someone thinks but something that can actually be verified and confirmed. The sky is blue is a fact if the sky is actually blue right then, while the comment :I think blue is unattractive” is not a fact but an opinion. Facts are not subject to the whim of the person compiling them, they do not change without proof or evidence.
Facts are stupid until brought into connection with some general law.
Facts are the air of scientists. Without them you can never fly.
Facts sometimes have a strange and bizarre power that makes their inherent truth seem unbelievable.