1.nounThe series of vertebrae, separated by disks, that encloses and protects the spinal cord, and runs down the middle of the back in vertebrate animals.
2.nounAny fundamental support, structure, or infrastructure.
"Before automobiles, railroads were a backbone of commerce."
3.nounCourage, fortitude, or strength.
"He would make a good manager, if he had a little more backbone."