C, L, and R scattered throughout this play?

Hi. I literally just joined this forum cause I can't find an answer to this anywhere on Google. Which seems sort of silly at this point in history.
The question:
I'm reading Lady Windermere's Fan by Oscar Wilde. In the brackets, there always lie a few R's and L's and C's. Example: "[Exit Parker C.]" or "[Still seated at table L.]"
What the hell do they mean??

Please please help me, this is driving me insane.

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C, L, and R scattered throughout this play?