Stage Directions

Onstage is anything that the audience can see, while offstage is anything the audience cannot see. 

Offstage is anything that the audience can see, while onstage is anything the audience cannot see.

Onstage is anything that the actors can see, while offstage is anything the actors cannot see.

director's

actor's

audience's

... actors would look "down" at audience members.

... directors would have to point "up" or "down" to give directions. 

... stages used to be slanted, so "up" and "down" were literal descriptions. 

... the direction that the audience reads from.

... the location that an audience member is sitting. 

... the side of the stage that the spotlight is on. 

If you are on stage, the directions are backwards from your POV.

If you are in the audience, the directions are backwards from your POV.