Question

This is a small structural unit of a play. it is a single unit of thought. a director will divide dialogue into these units to understand the play moment-by-moment. what are these units called?

Answer 1

I believe the answer is: Beats.
In this context, beats refer to  unit of script analysis that represent the smallest form of actions that written in the play script.
The story in the play would be developed through the collection of beats that initiated by the characters.