Which word best describes something that is known widely?

The term that best describes something known widely is "common." This word indicates that the subject is prevalent, easily recognized, and broadly understood or encountered by many people. In contrast to "familiar," which suggests personal recognition or comfort with something, "common" implies a more universal presence in society. The other terms do not align with this meaning: "rare" indicates scarcity or infrequency, while "obscure" refers to something that is not well-known or understood. Thus, "common" effectively captures the essence of widespread knowledge.