A
beat is a scene or a small section of a scene in which a
character attempts to achieve his or her objective. For
example, if there is a husband and wife scene, the two may
be arguing about the fact that the husband had an affair.
The wife makes a point. The husband makes a point. The
wife makes a different point. The husband apologies. Each
point that is made between the two is a beat because each
character used that particular section of the scene to
accomplish the objective of getting their point across.