This has been a concern of mine for a long time, but now that I'm documenting the manual I'm finding it even more difficult to know what term should be used when referring to the Properties Region (aka "N-panel", "properties panel", "properties bar", "N-shelf" etc...)
I would like to propose that we make a formal decision and stick to it, both in tooltips and the user manual.
At the moment I'm under the impression that "Properties Region" is the correct term - if so, here is a patch which hopefully corrects all the tooltips and code comments in Blender which refer to it as the "properties panel" (note: although I do not know for sure what to call it, I do know that it is most definitely not a "panel"): http://www.pasteall.org/56638/diff.
And here is a similar patch which corrects the Addons-Contrib repo: http://www.pasteall.org/56637/diff - I found no obvious issues in the regular Addons repo.
My thoughts are that we should move away from the word "properties", as this is already used for the Properties Editor and has thus caused plenty of confusion.