Ok, a misfire is when a cylinder doesn't fire at the correct time, or at all. Typically its like a little popping, or a lack of noise. (you'll hear the engine drop off for a tiny second.) It'll sound like its stumbling.

A shop will pressure check it for you, and it shouldnt cost very much. If you can, stop by a parts store and make sure you arent pulling any SES codes (check engine.)