Ooooof, this is going to be difficult. Not only are we dealing with the Middle Ages, which laughs at all conceptions of 'fixed' borders between almost literally anything, but we must also face, as you're already aware, the sheer variety in both locale and timeframe. I am reasonably sure there's more answers here that I haven't managed to catch with my search terms, and as always, anyone who wants to contribute further, especially about how it went for other regions and time periods, is more than welcome to do so. The non-nobles of the Medieval Era deserve whatever voice we can give them.

First off, some generalities:

• u/butter_milk explores the relevant division between some of the terms,
• u/Flanwaw provides a more recent look at the same division, with augmentation by u/Rittermeister.

For the more focused stuff, see next post.