common knowledge - Wiktionary, the free dictionary

From Wiktionary, the free dictionary

common knowledge (uncountable)

1. That which is known by most people, and thus cannot reasonably be contested.
2. (logic, game theory) A special kind of knowledge for a group of agents, such that when all the agents in a group G know p, they all know that they know p, they all know that they all know that they know p, and so on ad infinitum.

• common knowledge on Wikipedia.Wikipedia