Unsolved means not yet figured out or explained. When a mystery remains unsolved, nobody has discovered the answer yet, even though people may have tried hard to solve it.

Detectives work on unsolved cases where crimes haven't been explained or where criminals haven't been caught. Scientists tackle unsolved problems in fields like mathematics or physics, where certain questions have stumped even brilliant researchers for decades or centuries. The Riemann Hypothesis, for example, is a famous unsolved mathematical problem that has challenged mathematicians since 1859.

Sometimes puzzles or mysteries stay unsolved because they're incredibly difficult, requiring new tools or ways of thinking that haven't been invented yet. Other times they remain unsolved because crucial information is missing or lost to history. Ancient civilizations left behind unsolved mysteries like the purpose of certain monuments or the meaning of undeciphered writing systems.

The word carries a sense of challenge and possibility. An unsolved problem isn't impossible, just not conquered yet. Many problems once considered unsolved eventually yielded to persistent effort and creative thinking. What's unsolved today might be tomorrow's breakthrough.