A beat is one of the most basic elements in storytelling. It refers to a significant story moment or shift in a script. For instance, a character finds a ticking bomb in their car or a dead body in their basement.
That being said, a beat doesn’t have to be a life-or-death moment. It’s simply a moment that clearly propels the story forward. However, because beats are the building blocks of storytelling, they typically do not have smaller constituent parts.