Why were men called Pilgrim fathers?

The Pilgrims were a group of religious separatists who left England seeking religious freedom and a means of maintaining a distinct communal identity. It was the Pilgrims (literally meaning travelers) who landed at Plymouth, Massachusetts, and began the European settlement of that region of what is now the United States. They are called the Pilgrim Fathers because they were the parents (biologically at first but later only in a general historical sense) of most of the population who came to live in that region.