We obviously use the word "discipline" to mean different things. For me it's something like "stop talking loudly while the teacher is trying to explain a difficult concept to your classmates".

As an illustration, here is a quote from my favourite blog about teaching:

A teacher in a British school is likely to be used to starting to do something, even something as simple as speaking, and having to stop what they are doing due to deliberate disobedience. If you are not a teacher it might be hard to imagine how frustrating this defiance is. I can only suggest that you imagine that feeling you get when you are in a traffic jam on an important journey. Now imagine how you feel when you think the traffic is starting to move on, only for it to grind to a halt a second later, and imagine that happening repeatedly for hours on end. Now imagine how you feel when you realise that the hold-up is not actually due to an accident ahead, or a busy road, but is in fact due to somebody (probably a caravan owner) deliberately driving at 10mph in front of you and not letting anyone overtake. Now imagine that you are trapped in this situation for two dozen hours a week. Finally, imagine that every so often your boss drives up to your window and tells you that if you are trapped in a traffic jam it must be because you are a crap driver. If you can imagine that, then you have some idea how frustrating it feels to be a teacher.