One of the actualities of academia that is important to be aware of when using this site is: Academia varies more than you think it does. More explicitly: Academic practices strongly vary between countries, fields, journals, universities, departments, and even groups. It is easy to arrive at the false conclusion that some aspect of academia is the same everywhere.
This is a problem that pertains to all levels of users on this site:
Questions whose answers depends on the culture and regulations of individual institutions (that operate below the national level) cannot reasonably be answered by us (or any other similar Internet site). We close such questions since we have become tired of having a bazillion answers whose only substance is: “it depends”.
Answers that assume that academia is homogeneous in some respect when it is not are at best confusing to some readers and wrong and misleading at worst.
I already noted this in my answer to Welcome to Academia SE, which got insanely popular. However, given the restrictions and purposes of that question, it contains only a list of the most important examples – which is already quite long for something that is supposed to be a short introduction. Yet, due to the above problems, an extensive list of inhomogeneities in academia would be a valuable resource for the users of this site. Hence I am asking:
In which respects does academia vary more than many people expect?
Variations can be along different axes, e.g., between fields, countries, journals, universities, departments, or groups.
Answers shouldn’t be an obvious consequence of the differences of subjects, countries etc., e.g., it is little surprising that work groups in theoretical physics don’t refer to themselves as labs, or that research in poorer countries focuses on less expensive subjects.
Group answers into reasonable categories, roughly per tag on the main site. If you have something to add that does not fit into the existing categories, add a new answer (and link it in the table of contents below).
When possible, link to relevant posts on the main site.
This is a community wiki. Please feel free to contribute.