Nothing in the Constitution defines the term either. Rubio is a natural born citizen because he was born here.
DD, these comments are not personally directed at you.
But this is a question I have.
How can a 14th Amendment anchor baby be equivalent to a natural born citizen?
When Rubio was born, what jurisdiction was he subject to?
The United States or Cuba?
Which jurisdiction were his parents subject to?
Natural born has a meaning, and Rubio does not fit it.
He did not even have one American parent.
Being born here makes him a native born citizen, but not a natural born citizen.
As for definitions in the Constitution, the term Letters of Marque is not defined either. But we know the meaning.
After 1868. That's important because that's when men changed the laws of nature.