Definition
1) An issue of fact, not law. A question of fact is resolved by a trier of fact, i.e. a jury or, at a bench trial, a judge, weighing the strength of evidence and credibility of witnesses. Conversely, a question of law is always resolved by a judge.
2) In some jurisdictions, an issue regarding the determination and/or interpretation of foreign law in a case. A party seeking to rely on foreign law must prove it like any other fact that has not been judicially noticed. In some jurisdictions, a question of fact regarding the determination and/or interpretation of foreign law is resolved by a jury or, at a bench trial, a judge.
Illustrative caselaw
See, e.g. Markman v. Westview Instruments, Inc., 517 U.S. 370 (1996) (regarding questions of fact generally) and Griffin v. Mark Travel Corp., 724 N.W.2d 900 (Wis. Ct. App. 2006) (regarding foreign law).