Sequence

The screenplay is comprised of a series of elements that can be compared to a system, a number of individually related parts arranged to form a unity, or whole:  Like the solar system.  A screenplay is really a system of sorts, comprised of specific parts that are related and unified by action, character, and dramatic premise. 

The screenplay, as a system, is made up of specific elements:  end­ings, beginnings, scenes, Plot Points, shots, special effects, locations, music, and sequences.

The sequence is perhaps the most important element of the screenplay. 

A sequence:  A sequence is a series of scenes connected by one single idea with a definite beginning, middle, and end.

It is a unit, or block, of dramatic action unified by one single idea. It is the skeleton, or backbone, of your script and, like the nature of structure itself, holds everything together.  like a chase sequence, wedding sequence, party sequence, fight sequence, love sequence, storm sequence.

You begin writing your screenplay, you need to know four things:  the opening, the Plot Point at the end of Act I, the Plot Point at the end of Act II,    and the ending.
Sequences can be written any way you want; they are a creative, limitless ..context within which to paint your picture against the can­vas of action.  Writing an action sequence is a definite skill, and good action scripts are written with color, pacing, suspense, tension, and, in most cases, humor.

 source : Syd field Screen play -The foundations of screen writing