what's the difference between plug-in, hook and hack-in?

[TaMpE]

I was reading this : https://vborg.vbsupport.ru/showthread.php?t=82625

and found a few things that messed up my understanding and also fixed my other confusion but since there's new confusion, I want to know that difference before I choose the wrong path in case I get a larger forum.

Second thing, hooks will not get you into every corner of the code. Some things will always be done best with a hack. For example if you are looking to add something but need to query the db for some extra data and want to avoid and extra query (in other words you are going to modify an existing one with a join or such) forget it and hack it in, there are no hooks that let you modify existing queries.

Last but not least hooks are not magic, don't add a million of them and expect your forum to run as fast as it did when you first installed it. Only plug-in/hack-in what you really need!

and BTW, do all XML addon/mods we see here have <hookname>?