The reason the word 'screenplay' is not used much in live theater is because there are no special instructions for producing the work on a screen or in a film medium. The screenplay includes those aspects of filming that are outside the actor's purview, things like camera angles and cut or fade instructions, effects that the audience will see but have no effect on the actor's performance while on set. It may very well be the 'shooting script' in most cases, which is less of an actor's tool and more of a director's tool. The screenplay is the extra layer with everything that was left out of the script. But, anything not directly impacting the performance are generally left out. What sound effects or lighting effects that are important to the actor's performance are noted. The primary focus here is on telling the story, the word and actions that convey the message. This is similar to the 'spec scripts' given to agents and producers to generate interest in the work. The script that the actors use during filming contains primarily dialogue with minimal stage direction. The main difference between usage in the terms 'screenplay' and 'script' is the function of the document.
