What term describes freeborn Roman citizens when classified socially?

The term that describes freeborn Roman citizens when classified socially is "Ingenui." This classification specifically refers to individuals who were born free and were considered as full citizens with the associated rights and privileges in Roman society. Ingenui had the ability to participate in political life, own property, and were subject to the laws of the Roman Republic.

The other terms listed can be understood in the context of Roman social structure but refer to different aspects. "Plebs humilis" refers to the lower class of common people who may not have the same standing or privileges as the ingenui. "Augustales" were priests responsible for the worship of the Roman emperor, highlighting a specific religious and social role rather than a broad classification of citizens. "Scriptores" refers to writers or authors, which does not pertain to the classification of social status among Roman citizens. Therefore, ingenui is the most accurate term to describe freeborn citizens in the Roman social hierarchy.