A term used in theater. It is what the playwright literally gives the character he creates. If in the stage directions the playwright says that Sam is a 30-something overweight unsuccessful man, then we know Sam is a 30-something overweight unsuccessful man.

But, we do not know that Sam eats 10 Snickers a day, that Sam works at Dairy Queen, or that Sam is precisely 36 on Tuesday.

A Given Circumstances does not need to be stage directions. Dialogue example:

Betty: How's the husband?
Sue: Fine, and the boyfriend?
Betty: Broke up last night.
Sue: Oh I'm sorry.
Betty: You're my only friend.

From the dialogue we know that Betty has a husband (unless later in the play we discover she is lying.) Sue recently broke up with her boyfriend. That Sue and Betty are friends.

With dialogue one must be more cautious because the characters could be lying to one another, but through the course of the play one should be able to discern when characters are lying or not. Given Circumstance is solid information. If their is no reason to dispute or no other options about a character it is Given Circumstance.