Which word describes something that is established as a common practice or tradition?

The term that describes something established as a common practice or tradition is "norm." Norms are the unwritten rules and expectations that guide behavior within a group or society, often developed over time and reflecting shared values. They play a crucial role in social interaction, as they help individuals understand what is considered acceptable or typical behavior in various contexts.

While "ritual," "rite," and "protocol" can also refer to established practices, they possess specific connotations or contexts that differentiate them from the broader concept of a norm. Rituals often imply a ceremonial aspect, rites are usually formal, often religious, procedures, and protocols establish formalized procedures or guidelines, especially in contexts like law enforcement or organizations. In contrast, a norm encompasses a wide range of common societal behaviors that may not necessarily involve formality or ceremony.