The Meaning of Frontier
For a lot of scholars the time of the frontier lasted from the foundation of Jamestown in 1607 until 1890, when the frontier was officially closed.
frontier is derived from latin "frons" "frontis".
"fronter" over old french meaning to stand out, to protect.
But what now is the frontier?
Originally it was the front line of the army. In U.S. history, it was the westward moving sphere which divided civilization from wilderness.
The frontier had been separating the regions with less than two, from those with more than two people per square mile.
It played a huge role in the Americanization of the settlers.
Sources: Turner, Frederick Jackson. The Frontier in American History. New York: Holt, Rinehart & Winston, 1962.