Sta. Maria del Fiore, or the "Duomo" by which it is most often called, is the Cathedral of Florence.
Italian cities have any churches, but only one Cathedral, which is the seat of the Bishop of that city.
The term "Cathedral" comes from the Latin word "cathedra" which means chair or seat... in this instance, "seat of the Bishop".
In some Italian cities, the Cathedral is also known as the Duomo, or House of God.

This image is a good example of the need for a wide-angle lens in Italy.
The piazza where the Duomo is located in Florence, is small, and it is quite difficult to get a full shot of the church and adjoining bell tower.
My image shows part of the Duomo's facade, the monumental dome designed and built by Brunelleschi in the mid 1400's,
and part of the adjoining bell tower.