Unexplained means not accounted for or not made clear. When something remains unexplained, no one has figured out why it happened or how it works.

If a window breaks in an empty classroom and no one saw what happened, the broken window is unexplained. When scientists discover ruins of an ancient civilization but can't figure out why the people abandoned their city, that mystery stays unexplained. A sudden noise in the night that you can't identify is an unexplained sound.

The word suggests something puzzling or mysterious that needs an explanation but doesn't have one yet. Sometimes things are unexplained temporarily, like when you get an unexplained headache that your doctor eventually traces to not drinking enough water. Other mysteries have remained unexplained for centuries, like exactly how the ancient Egyptians moved massive stone blocks to build the pyramids.

Notice that unexplained doesn't mean unexplainable. Many things that were unexplained in the past, like what causes lightning or why people get sick, now have clear scientific explanations. When something is unexplained, it means we haven't found or been given an explanation yet, not that finding one is impossible.