"Giovanni Mastai-Ferretti" is a name that belongs to Pope Pius IX, the longest-reigning pope in history. This name has various synonyms that are often used to refer to him in different contexts. Some of the synonyms for Giovanni Mastai-Ferretti include "Pio Nono," a nickname that was given to him during his papacy, "Papa Pius IX," "Giovanni Maria Mastai-Ferretti," and "Pope of the Immaculate Conception." Each of these synonyms highlights a different aspect of Pope Pius IX's life and legacy, demonstrating the many layers of meaning that can be found in a single name.