What it means

1. noun the part of a network that connects other networks together
   “the backbone is the part of a communication network that carries the heaviest traffic”
2. noun fortitude and determination
   “he didn't have the guts to try it”
3. noun the part of a book's cover that encloses the inner side of the book's pages and that faces outward when the book is shelved
   “the title and author were printed on the spine of the book”
4. noun the series of vertebrae forming the axis of the skeleton and protecting the spinal cord
   “the fall broke his back”
5. noun a central cohesive source of support and stability
   “faith is his anchor”