I came across the word "proper" while reading a random comment on a video about WW2 Japanese history on YouTube.
Showing even more dedication to their ideology was when Americans started landing on Japan proper, both civilians and soldiers committed suicide rather than be taken prisoner.
I looked the word up on Lexico.com. This what it gave:
part of speech: adverb, British informal dialect, definition--satisfactorily or correct
At first, I thought proper meant exactly like the Lexico entry said but I was still confused.
Next, I looked up the word in the Collins Dictionary and I got this:
You can add proper after a word to indicate that you are referring to the central and most important part of a place, event, or object and want to distinguish it from other things that are not regarded as being important or central to it.
Example: A distinction must be made between archaeology proper and science-based archaeology
I still am confused. Please explain what the word "proper" means, whether in the context of the YouTube comment or in a general context.