Were citizens in ancient Rome the same as commoners? What are their differences and connections?

Not the same.

Generally speaking, Roman commoners refer to citizens other than Roman nobles. It seems that sometimes it can also refer to free people other than nobles (that is, including non-citizen free people). Citizens included senators and nobles. Citizens of Rome had many political and economic rights.

To put it simply: The people with the right to vote in the Citizens’ Assembly are citizens, and citizens must be free people, not slaves. Nobles are above common people and have more privileges than ordinary citizens. Common people definitely refer to a group of people who are neither slaves nor nobles. Whether it refers to common people among citizens or includes people other than citizens depends on the specific context. .