backbone
noun [ C, usually singular ]
uk/ˈbækbəʊn/ usthe backbone (of sth)
the most important part of something:
Small businesses are truly the backbone of the economy.
Imaginative ideas may form the backbone of your progress in the future.
COMMUNICATIONS, IT
the system of equipment and connections that allows communication at high speeds over long distances:
The company runs the biggest internet backbone in the US, carrying about 37% of data traffic.