A puzzle hunt is a set of connected puzzles, usually involving a story. Puzzle hunts sometimes hide the puzzles, e.g. what looks like a book about furniture might actually contain puzzles. And often no instructions are provided on how to solve a puzzle, or what to do with the solution. Typically, the solutions from all puzzles are required to solve one (or several) final puzzles, the so-called meta-puzzle.
The fun of a puzzle hunt is that you are not simply solving puzzles to solve a puzzle, but the solutions of the puzzle will unravel a story, or allow you access to more puzzles. It is also a great training opportunity for problem solving, and an excellent team activity.