Definitions of backbone:

• noun:   the part of a network that connects other networks together

  Example: "The backbone is the part of a communication network that carries the heaviest traffic"

• noun:   fortitude and determination
• noun:   the series of vertebrae forming the axis of the skeleton and protecting the spinal cord
• noun:   a central cohesive source of support and stability
• name:  A surname (very rare: popularity rank in the U.S.: #75296)