1. Rules or regulations that have been set up, agreed upon, or recognized as standard and accepted by a group, organization, or society
We must follow the established rules of the company.
Devemos seguir as regras estabelecidas da empresa.
2. Conventions or norms that are long-standing and widely accepted
The established rules of grammar are important for clear communication.
As regras estabelecidas da gramática são importantes para uma comunicação clara.