If you're trying to more narrowly say "all instructors are considered professors", that's not true at any institution type, not even R1 (major research Universities)
https://www.aaup.org/sites/default/files/10112018%20Data%20S...
I'm not sure what you're trying to say with that PDF - it doesn't even mention the word!
An associate professor would at least be tenure-track.
Have you never heard of 'adjunct professors' in the US?
> An associate professor
In most countries people at the level of just associate professor don't call themselves 'professor.'
> like some Ph.D graduates might insist on being called 'Doctor' even though they're not a medical doctor
The title 'doctor' means you have a doctorate, or in some cases like the UK it's also used as a courtesy title for a medical professional with just a bachelors degree. PhDs, EngDs, DPhils, DLs, MDs, and more are all entitled to use it as much as each other.
Is this different in the US?
I think in the US everyone just automatically gets the title 'professor.'
1. Assistant Professor
2. Associate Professor
3. [Full] Professor
As far as I know, you should only use the title "Prof." to refer to a "full" professor, and "Dr." for assistant and associate professors. In reality, everyone is just referred to as a "professor".
My University also has a few other titles: Acting Prof, Research Prof, and of course Prof Emeritus
All three types are generally referred to as "professor" but they differ in their seniority.
But it is reasonably common, unlike in (say) the UK.
You have instructor, assistant professor, associate professor, and professor. There's also such things as visiting professor (temporary postition) or professor emeritus (used to be a professor).
[0]. https://www.bu.edu/handbook/appointments-and-promotions/clas...
The link you gave says "The granting of Tenure, discussed in “Tenure and Promotion on the Charles River Campus”, is a separate guarantee that is not implied by any of the titles discussed in this section."
The tenure document, for example, says that 'The award of tenure to an Assistant Professor shall include promotion to the rank of Associate Professor.' So 'tenured associate professor' is a tenured faculty role, in addition to the 'tenured professor' faculty, such as http://www.bu.edu/wheelock/dr-leslie-dietiker-promoted-to-as... .
Perhaps there's a difference in terminology? My sense is that in academic circles, adjunct is now frequently used not for a specific position/title, but for the class of professionals who are hired on a semester by semester basis and paid by the class. Whereas the assistant/associate/full professor ladder is well defined most places, the adjunct position is more of an afterthought. It's temporary/disposable labor.
In my experience it's a professional affiliation that is flexible, designating that you are not a student, but not regular faculty. In some cases it designates a sessional lecturer (i.e. paid by the course, not full time, no job security), but it can also be used to associate someone in the department for the purposes of contributing to research or co-supervising a student. So you can end up being an adjunct for a department for a while without ever having been employed by them directly.
Originally it was much more the latter use, and not the former, but as the use of non-TT instructors grew some places used adjunct for this, others "lecturer", "sessional" etc.