Apart from what's written in the help center, if you have a question, ask yourself whether it concerns the specific site or the whole network.
On a site meta, questions about the site's scope and policies are on topic. Also requests to close or reopen questions, tags etc. These are all topics that each stack has to decide for themselves (or already did).
On MSE, ask questions that concern other sites, too. For example, feature requests that would bring a change for every user on the network.
E. g. let's look at your previous question about the rejected edit. It was about the mechanism underlying the suggested edits review process and so it was fine to post here. If you had wanted to know why your edit was rejected, Ask Different's meta would have been more appropriate instead, because it is more about a site's policy.
There is sometimes some overlap. For example, you could start a discussion on a possible feature on a site's meta and see if you can get support. And if you got it, you can take it to MSE. Here is an example.
Maybe to expand a bit on Bart's comment: This was once (also) the meta for Stack Overflow. Here is the post announcing the split into Meta Stack Overflow and Meta Stack Exchange. That's also why you can still find old posts that are pretty SO-specific (talking about tags, or why a question was closed / deleted etc.).