''Production still''

Dear All,

I’ve done a bit of search into what production still means and I’d like to ask if I understand it right.

So, it can be simply a snapshot from the film, like when we pause a video, or can be a photo portraying the crew as well while working, or can be a posed picture that is made separately from the film either during it or not, and either with a composition that occurs in the film, too, or not.

On the other hand, it can’t be a posed picture of the actors and the crew together, if I get it right.

Could you, please, tell me if my two statements above are correct? And what is meant by the term most of the time? Thank you in advance!