What is a professional student, in the context of a "Graduate and Professional Student Organization" in the United States (cf. this one)? How are they different than or similar to post-docs?
While Bill Barth's description of "professional student" as someone whose sheltering in academia and trying not to graduate is one I have heard, there's also a more formal designation for the term.
Mainly, post-graduate students who are in professional degree programs. For example, medical and dental students, law students, many students pursuing Masters of Public Health degrees, or MBAs, etc. are all pursuing degrees that are intended to be applied to a profession, rather than going further into academia. They often have somewhat different concerns than graduate students, hence the different term.
My experience with the term is frequently derogatory. It is usually applied to a person who either doesn't know what they want to study, switches their major every year or two, refuses to graduate, and spends many more years than the average in school before graduating. Or, slightly less bad, is someone who likes school so much that they keep finding ways to get degree after degree after degree, never getting a job related to one of their majors, and typically working menial jobs to keep funding their education habit.
Without knowing the exact details (e.g. country, university, link to that organization's website), I would wager the following presumption:
This is an organization of those students who are more experienced, mature or advanced relative to the regular/typical undergraduate students. One category of these are graduate students, another is students who are established professionals outside academia - either due to work experience or a non-academic qualification - and are engaged in some kind of supplementary or advanced study programs.
Examples of potential such "professional students":
- Performance artists
- School teachers
in some countries these might fall under the "graduate student" category, but in others the qualifications for these professions are not undergraduate academic degrees.