The Catholic Church is modeled after the Church in the Bible, which means that it's organized according to cities and territories. As we read in the New Testament, the Apostle Paul addressed his letters to the churches at Rome, Corinth, Galatia, Ephesus, Phillipi, Colossi and Thessalonica. These were cities around the Mediterranean Sea.
Now, cities can be big places, and churches may not be able to meet all in one place at the same time. Large gatherings attract a lot of attention, and this was not practical during times of persecution. Therefore, Christians of one church often met together in separate locations. A bishop oversaw the whole city church, while he employed presbyters (elders or priests) to oversee small congregations in various locations throughout the city. When the Apostle Paul wrote to a city church, it was addressed to the bishop, who read it first and then shared it with the presbyters, who then read it to their small congregations.
This is how the Catholic Church is arranged today, more or less, throughout the world. Here in the Ozarks, there are not many Catholics. So our city churches tend to span large swaths of territory to cover the Catholics spread out therein. There are four Catholic dioceses (city churches), and two personal ordinariates, that cover the Ozarks. A diocese is a fancy word for the kind of city church we read about in the Bible. The word diocese comes from the Greek word dioikesis (διοίκησις) which means "administration." A "personal ordinariate" is the name of a special jurisdiction for Catholics who (for various reasons) don't fit into the normal diocesan structure. All Catholics are in full-communion with each other, regardless of jurisdiction. A jurisdiction simply determines who your bishop is.