What is the "chalk talk" at job interviews? It was only recently that I heard about the academic "chalk talk" at job interviews (from biologist friends). As I understand, this is a closed-doors talk the applicant must give to the existing faculty. I was shocked that even through I am preparing to apply for faculty positions, I never heard of this practice before.

So my questions are:


What is this "chalk talk", and how common is it at job interviews?
Is it specific to biology, or at to least experimental fields? Almost all the information I can find about it online is focused on biomedical sciences (and the few articles that don't, still assume an experimental field). Perhaps the concept exists in other fields too but people use a different term than "chalk talk" to describe it?
My work is in one of the hard sciences and is purely theoretical. What are the main differences between experimental and theoretical (mathematically oriented) fields in how this chalk talk is given? Since most of the online advice I found concerned biology, I need to decide how much of it is relevant to me.


Update:

Many of the comments (and one answer) show that several people have completely misunderstood my question.  I would like to emphasize once again that the question is about the specific part of faculty position job interviews referred to as "chalk talks".  In the meantime, I found a hint that this concept might be specific to life sciences.  My question is not about lecturing techniques with white- or blackboards, nor about why this part of the interview is called a "chalk talk" (i.e. etymology).  

It's about what this part of the interview is about, which fields have this as part of the job interview protocol, and what differences are there between biology and theoretical (math/physics) fields (i.e. what part of advice given by/for biologists should I take or ignore).

Here is an example of a blog post discussing interview chalk talks.
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).