backbone

The series of vertebrae forming the axis of the skeleton and protecting the spinal cord.

Fortitude and determination.

A central cohesive source of support and stability.

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 part of a network that connects other networks together.

“the backbone is the part of a communication network that carries the heaviest traffic”