In screenwriting, the Exposition is the information given, usually in the very beginning of a story, about the setting, conflict and the characters related to said conflict.

Usage

Exposition, when used during the Setup of a screenplay, should always be "handled" with great care for the screenwriter certainly does not want to give away too much about any one character or event. So, in essence, introduce the characters related to a conflict, the setting and enough information to whet appetites, then move on with the storyline. Now, during the course of the screenplay, exposition is usually used in the form of presenting backstory, but again, to use sparingly.

Format

Within the Setup there are obviously introductions of characters that will be related to a particular conflict, so basically, if you've created your Setup correctly then you've got your Exposition.