In ancient Rome, what sea was referred to when they spoke of "mare nostrum"?

Mare Nostrum was the Roman name for the Mediterranean Sea. In the years following the Risorgimento, the term was revived by Italian nationalists, who saw Italy as a successor state to the Roman Empire and therefore should regain control of the former Roman territories in the Mediterranean.

In ancient Rome, after the conquest of Sicily, Sardinia, and Corsica during the Punic Wars fought against Carthage, the term Mare Nostrum was used to refer only to the Tyrrhenian Sea. By 30 BC, Roman rule extended from the Iberian Peninsula to Egypt, and the expression Mare Nostrum began to be used to refer to the entire Mediterranean. Other names, such as Mare Internum ("Inner Sea"), were also used to refer to this sea; the expression Mediterraneum Mare is only attested after the fall of the Western Roman Empire.