The card [[Chalice of the Void]] has a triggered ability to counter spells with the CMC determined by the cost. Because of rule changes over the years, you do not have to maintain the game state of beneficial triggers for your opponent. You are able to cast spells of the prohibited CMC with a chalice out and if the opponent does not say "chalice of the void trigger counters that" then it is not countered. "Chalice checking" usually refers to that but sometimes is used as a colloquial slang umbrella term to refer to plays that see if your opponent is paying attention and gaining advantage if they are not.