What is the difference between NavMesh and PathFinding?

I’m new, so do not Flame me for this. I understand PathFinding, and A-Star method for find a path from point A to B. NavMesh appears to be a form of collision detection. In other software you set an object Class to be collidable and then your objects can bounce off it, or get stopped by it. In videos I see on line, it looks like NavMesh REPLACES the A-Star method, so we do not have to code path finding. Is this true? Do we still need a Path Finding solution, and just treat NavMesh as a quick form of collision detection? Say… I have 100 Balls in a scene, and a Magnet I can click on and off, and move. Do I just tell the balls to move to the magnet’s location, or do I need to PathFind? If PathFinding is needed in Unity 4, please suggest some fast scripts, that can handle 100+ balls, finding their way through a maze. Thanks. -FZ