A mystery is something unknown or puzzling that needs to be solved or explained. When your favorite snack keeps disappearing from the pantry and no one admits to taking it, that's a mystery. The word can describe anything from a missing homework assignment to deep questions scientists haven't answered yet, like what exactly happens inside a black hole.

Today, it mostly means something hidden or unexplained, though churches still use phrases like the mystery of faith to describe things about religion that go beyond ordinary understanding.

A mystery novel or mystery movie follows someone (usually a detective) trying to solve a puzzle, often figuring out who committed a crime. Sherlock Holmes stories, for example, are classic mysteries where the detective pieces together clues that don't make sense at first. Many people love mysteries because that moment when everything finally clicks into place feels wonderfully satisfying.

In everyday conversation, you might call someone mysterious if they seem secretive or hard to figure out. Scientists use the word when they encounter phenomena they can't yet explain, like the mystery of how birds navigate thousands of miles during migration. Some mysteries get solved quickly, while others puzzle people for generations.