Extremely remote. For example, John's about to move to some tiny island, truly back of beyond. This term, used as a humorous exaggeration, relies on the meaning of beyond (or the beyond) as “a distant place, beyond human experience.” [Early 1800s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
How to use back of beyond in a sentence
And, as the documentary illuminated, she worked, worked, worked—even if it meant going to the back-of-beyond venues.
You've been having high old times in that back-of-beyond town of yours, haven't you?The Borough Treasurer | Joseph Smith Fletcher