Most people talk about plot in the abstract. To me, it’s literal. I plot out the interactions of my characters on graph or line paper. That way, I can see which characters are interacting with whom from scene to scene. The more characters involved in solving the protagonist’s problem, the better the story. If a character is not moving the story forward, then the character is unnecessary.
One of the best definitions of plot is this: visual, interrelated action. Especially in a movie, it has to be visual. Thoughts or sensations can be plot elements, but only in books. In movies, it’s all about what characters say and do. E.M. Forrester gave a nice example. “The king died and then the queen died is a story. The king died, and then queen died of grief is a plot.” He was talking about books, of course.