Background questions are considerably broader and when answered, provide general knowledge. For example, a background question such as, "What therapies reduce postoperative pain?" can generally be answered by looking in a textbook.
Stillwell, S. B., Fineout-Overholt, E., Melnyk, B. M., & Williamson, K. M. (2010). Evidence-Based Practice, Step by Step: Asking the Clinical Question: A Key Step in Evidence-Based Practice. AJN, American Journal of Nursing, 110(3), 58-61.