What does "a falling out" mean?

I think drifting apart from someone is worse than falling out – when you fall out with someone you know you have to fix it, and all you have to do is say sorry. Drifting apart is so subtle that you don’t notice it for a long time, and by then you’ve lost the motivation to speak to that person again.

I have to say I don’t totally agree with that two best friends would decide to end their friendship only for a falling out. They could find a way to reach a agreement as long as they regard each other as their best friend.

I wouldn’t never have thought that it might be disagreement and end of the relationship. I thought about it as a tooth fell as it was making so much pain and his brothers and sisters had to get rod of him with this finishing the tooths happy existence. Make sense then!;)