Earlier quoted context omitted.
Could you elaborate a bit? I know that over here there are certain requirements (needs to teach classes, publish at least one paper a year). Is this different in the US?
There are multiple 'professor' titles, but only one tenured faculty role. The tenured faculty is the holy grail, and everyone else is underpaid and overworked. [0] 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/…
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... .