Icebreaker

noun

1. A ship designed to break through ice so that it, or other ships coming behind, can navigate on frozen seas.

   "The steel hulls of ice-breakers are much thicker than those of standard vessels."

2. A game, activity, humorous anecdote, etc., designed to relax a group of people to help them get to know each other.

   "The new college hallmates were awkward with each other at first, but after a game of charades as an icebreaker, they were laughing like old friends."

3. A lively song and dance routine at the start of a musical.