One of the pillars of the Roman Catholic Church is the establishment of dioceses in almost all the countries all over the world. But what is a diocese?
What is it?
A diocese is a district of the Roman Catholic Church under the control of a bishop or archbishop. A diocese is made up of smaller parishes which each have their own churches. A diocese managed by an archbishop is often referred to as an archdiocese.
Diocese vs. Archdiocese
The difference between a diocese and an archdiocese is deeper than simply who leads it. An archdiocese typically has a larger Catholic population under it than a normal diocese.
How did it come about?
Originally, the term diocese was used politically by the ancient Roman Empire to refer to an organized group of provinces. After Christianity had been declared as the Empire’s official religion in the 4th century, the term gradually shifted its meaning to that of a religious district. Following the fall of the Roman Empire in the 5th and 6th centuries, the bishops took over administrative roles of the former Roman prefects over their respective districts.
What is the function of a diocese
A diocese’s main function is to organize parishes. It is headed by a bishop who extends his influence to his priests and pastors, who each in turn manage the parishes that make up the diocese. In comparison to the Pope, who has complete, supreme authority over the Catholic church, the bishop’s power extends only to his own diocese and the parishes underneath him.
While serving as extensions of the Pope, bishops and archbishops have to make trips to Rome every five years in order to report the situation in their respective dioceses to the Pope directly.
What kinds of dioceses are there?
There are six kinds of dioceses:
The Papal See is the diocese of Rome, under the jurisdiction of the Pope. A patriarchate is a diocese ruled by a patriarch, the highest-ranking bishop in the Catholic Church. A major archdiocese is one ruled by a major archbishop. A metropolitan archdiocese which is an archdiocese in a metropolitan area. An archdiocese, under the jurisdiction of an archbishop, and your typical diocese under the power of a bishop.
How many dioceses are in the world?
As of April 2020, the Catholic Church reported almost 2,900 regular dioceses, with 1 papal see, 9 patriarchates, 4 major archdioceses, 560 metropolitan archdioceses, 76 archdioceses, and 2,248 dioceses.

Thanks for the informations but I am still confused about the difference between a metropolitan archdiocese & a major archdiocese.