What is the 'Macbeth' curse, that Twitter users suggest got Chris Rock slapped?

As per an old superstition, the word 'Macbeth' should never be uttered in a theatre, or else it brings bad luck. The superstition has often caused people to refer to it as 'The Scottish Play'. Notably, Chris Rock had said 'Macbeth' a few minutes before Will Smith slapped him on the Oscars stage, leading users to draw this theory.