Tacit collusion is a collusion between competitors, which do not explicitly exchange information and achieving an agreement about coordination of conduct. There are two types of tacit collusion - concerted action and conscious parallelism. In a concerted action also known as concerted activity, competitors exchange some information without reaching any explicit aggrement, while conscious parallelism implies no communication. In both types of tacit collusion, competitors agree to play a certain strategy "without explicitly saying so". It is also referred to as oligopolistic price coordination.