Stage blocking is when the director is guiding the actor’s movement and positioning on the stage. This term may be used during a performance of an opera, film, ballet or play.
A sightline is the line between the edges of the stage also known as the spectacle in a theatre or stadium or any sort of staging.
A stage direction is a order that is written in brackets on a script that tells an actor how to do something. This helps keep the show running without any major pauses.
When somebody says "Upstage" it means cover the back half of the stage. Staging directors are important because actors need to be able to know in which director they should approach and arrive so that they don’t clash between other actors.
Downstage is the opposite of upstage. It covers the front half of the stage and can also be used to direct actors.
Stage Right and Stage Left
Stage right and stage left is as stated the right and left halves of the staging area. All the stage terms cover the whole stage.