When people mosh, they dance in a wild, pushing way at a loud rock or punk concert. You do not take neat steps. You jump, bump into other people, and move in a tight crowd near the stage. That crowd is often called a mosh pit. The word is informal. Young people at loud shows use it; you would not use it about ballet, a school disco, or quiet pop. It can be a verb (they moshed all night) or a noun (a mosh). It feels rough and exciting, not polite. People who mosh usually treat the pushing as part of the fun — though actually it can still hurt, and many shows ask the crowd to pick up anyone who falls.