Definition of "borderland"

retaining Liddesdale and his other Borderlands and Offices in his owne person

1644, David Hume, The History of the Houses of Douglas and Angus‎, Edinburgh: Evan Tyler, page 81

some of the ancient East Lancashire families, whose mansions lie on the hilly border-land between the two counties

1850, Charlotte Brontë, letter dated 16 March, 1850, in The Life of Charlotte Brontë by Elizabeth Gaskell, London: Smith, Elder, 1857, Volume 2, Chapter , p.

They came to the river that marked the very edge of the borderland of the Wild […]

1937, J. R. R. Tolkien, chapter 19, in The Hobbit‎, New York: Ballantine Books, published 1966, page 282

[…] he pieces together his tale: arson, cattle raids, the usual borderlands story, ending in destitution, the making of orphans.

2012, Hilary Mantel, Bring Up the Bodies‎, New York: Henry Holt, Part 1, Chapter 2, p. 68

Is he [the Scotchman] orthodox—he has no doubts. Is he an infidel—he has none either. Between the affirmative and the negative there is no border-land with him. You cannot hover with him upon the confines of truth, or wander in the maze of a probable argument.

1821 August, Charles Lamb, “Jews, Quakers, Scotchmen, and Other Imperfect Sympathies”, in The London Magazine, volume 4, page 153

“Mr. Alwyn, the line between virtue and foolishness is dim and wavering, and I should hate to see you lost in that marshy borderland. […] ”

1911, W. E. B. Du Bois, chapter 25, in The Quest of the Silver Fleece‎, Chicago: McClurg, page 277

But she did not look as if she were dying; she looked as if she might go on existing in this borderland between life and death for ever.

1937, Virginia Woolf, The Years‎, New York: Harcourt, Brace, page 21

the subject lies in the misty borderlands of advancing knowledge

1955, Rachel Carson, chapter 2, in The Edge of the Sea‎, Boston: Houghton Mifflin, page 36

[…] he found himself in that frustrating mental state in which one is too exhausted to think productively and yet too alert to sleep, and in this restless borderland he lay for the remainder of the night […]

2019, Robert Harris, chapter 12, in The Second Sleep, London: Hutchinson