From BR Bullpen
The Boston Americans is the most-common name under which the American League team in Boston, Massachusetts was known from its creation in 1901 until it became the Boston Red Sox in 1908, a name it carries to this day.
During this period, the team was also known as the Boston Somersets and Boston Pilgrims, although these were "pet names" given by certain sportswriters without any official character. Retroactively, a number of publications list the team that won the inaugural World Series in 1903 as the Pilgrims, although it has since been demonstrated that no one used the name for the team at that time (its usage became more frequent in the following seasons, although by no means universal).
The name Americans refers to the League, and does not have any particular patriotic connotation. It was used to distinguish the team from the National League entry of the same time, usually known during that time frame as the Boston Beaneaters, Boston Doves or even Boston Nationals.