What is the "chalk talk" at job interviews?

I can't comment on how common this is outside of biomedical sciences (my field), but it's becoming quite common in this field.

In terms of what it is, the "Chalk Talk" is a chance for you to talk about your research (past, current, and future directions) without hiding behind Powerpoint slides.

You'll typically be given up to an hour to do this, in front of the hiring committee and/or faculty. You'll have a whiteboard/blackboard/flip-chart so you can draw down a key figure or two, or write an outline of what you're speaking about. It's less formal than a normal talk at a job interview - if you are asked to do one, expect to be interrupted and questioned throughout.

There are many reasons these are becoming popular. It's easy for candidates to talk through a deck of slides they've had weeks to prepare, and the hiring committee doesn't necessarily learn that much about them as people or scientists. This is more dynamic - it lets you see how people think on their feet - and gives a real opportunity for people to display their passion. It's daunting to speak for an hour with no props or prompts, but a good academic who knows their field, has a clear research plan, and cares about their work should be able to do this.

Source - personal experience (I have been on training courses specifically about giving chalk talks in faculty interviews, albeit in a different field).

Chalk talks are pervasive in the biomedical sciences in the US since the tenure requirements, at an R1, is to obtain an NIH R01 grant. Since the target funding source is known (unlike a lot of fields) and the applications are fairly formulaic, the chalk talk is really helpful. They allow the candidates to present a high level overview of a problem in the field, tell the committee about the 2 or 3 aims of their future grant proposal and discuss how the aims address the problem. The candidate can then use the board to draw up the results of the pilot studies that they will be conducting over the next 3 years in preparation of the grant application.

Since the pilot data don't exist yet and the committee is going to ask a lot of worse case scenario questions premade slides don't work well. A typical chalk talk might involve a candidate drawing a set of axis and a hypothetical line representing the pilot data that goes up. The first question from the committee might then be what happens if the data go down. Then a discussion about how the literature says it won't go down, but it might be a U shape and the line gets redrawn.

I don't think chalk talks work as well when there are a variety of funding sources. Industry money requires a different approach than an NSF application. It would be hard for the committee to judge whether the applicant is on the right track for funding.

The hiring process in different countries vary quite a lot. However, once you get an invitation to a job-interview, you can expect that institution will tell you what you should prepare. In case you are unsure, just ask your contact person the institution. And there are many things that are not standardized and it should be clear that an applicant can have quite a lot of questions (Who is going to attend the scientific talk? Will there be a demonstration of your teaching skills? Will there be students? Will there be a meeting with the dean/students/…? Do you have to prepare any additional documents in advance?)