The term "Yankee" (sometimes shortened to "Yank") have many different meanings. All refer to people from the United States. Outside the United States, "Yank" is used to refer to any American, including Southerners. Within the Southern United States, "Yankee" is a name which refers to all Northerners, or specifically to those from the region of New England, often in a mean way. The Oxford English Dictionary says that it is "a nickname for a person from New England, or, more widely, of the northern States generally." During the American Civil War, it was "used by the Confederates to the soldiers of the Federal army".
Elsewhere in the United States, it often refers to people from the Northeastern states, but especially those with New England cultural ties. This would include people who have colonial New England settler ancestors, wherever they live.