What's the word for...

[nacho]

In plays, such as the crucible,
you'll note that often to describe the actions of the characters,
preceding their speech, and succeeding their name, there will be something in square brackets.
for example
Danforth: [thinks, glances at Mary] "Is it true, child?"

I'm trying to use this in my essay, however do not know the word to describe it.
If you are confused as to what i am attempting to do, it is similar to addressing a soliloquy, to describe the character's inner feelings,
however yet, there is no actual speech or thought in these square brackets. so i assume it is, although similar, in many ways not a soliloquy.

[Spheniscidaphile]

is it just called Stage Direction?