[qingcharles]

Interesting that you mention that use. I've spent thousands of hours in court and never heard the term applied to expert witnesses, perhaps because their background is often stipulated.

The use the public would be most familiar with is the interrogation of the jury pool, by both parties, to make sure they are suitable (e.g. suitably biased) jurors before trial:

https://en.wikipedia.org/wiki/Voir_dire