I’ve come across it in various largely-Americentric writing and figured out the concept, but yeah, it’s not something I’ve seen practised in Australia.
It means “I will always be available in my office during such-and-such hours every week, for anyone to come and talk to.” I think it’s normally a walk-in affair rather than involving making appointments. First come, first serve, but now you don’t have to go through the bother of making appointments and such and comparing your timetables. Makes life easier for both parties. This article is talking of making appointments, but most of the benefits still remain of having a known block of availability.
A few of our lecturers had "office hours". It was a new phrase, and invariably they were younger and had worked in US universities. We could drop in between 3 and 5 one day a week to ask questions.
We thought them snooty.
The other faculty staff had an open door policy.
Now I'm their age, I appreciate how sticking to office hours helped these researchers to be productive. But as a student, open door flet more friendly.
In my experience, US professors generally were open door as well but it was about catching them being in their office. They could be lecturing, faculty meeting, lunch, etc, etc, etc.
Office Hours is a way of saying I will DEFINITELY be in my office at my desk during this block of time.
It is a common term in different areas, however not everybody here comes from an English speaking country and is knowing all English terms. For many English is second or third language.
In this case, you need to be American to make sense of this. And possibly you need to have been to a US university. Took me years of seeing people put a confusing number 101 on the end of guides on blogs or whatever before I realised that meant introduction to Americans.