In short, a Patron Saint is simply a saint that has been chosen specially to represent a group or a state or country, or something else.
Some other examples as well:
- St. Joseph is the patron saint of workers, because he himself was a worker who loved Jesus and Mary.
- St. Antony of Padua is the patron saint of lost things, because he lost a book, which eventually led to the return of a runaway fellow friar.
- St. Olaf of Norway is the patron saint of Norway, because he was a great Christian king, who evangelized his people and made Christian laws.
- St. Mark the Evangelist is the patron saint of Venice, because his relics were transferred to Venice.
- St. Thomas Aquinas is the patron saint of students and theologian, because he himself was a theologian, and his work, the
Summa, was used as a textbook of theology for hundreds of years (and still is).
These patronages are not as "official" as they might seem at first. And we are free to invoke any saint for any cause. However, some saints are called upon for special things, because of their association with a people, a place, a profession, a disease or even a miracle after death. Some people choose a saint for themselves as a "heavenly big brother/sister". And some people don'te care much at all about the saints.