What does ROOT stand for?

To answer this question the best is to quote René Brun , one of the project founders of ROOT, who gave this answer in 1996 in the ROOT mailing list:

At the start of the project in January 1995, I came quickly to the name ROOT for our system. The intention to move towards Object Oriented Technology was already well accepted at this time. It was clear to us that a basic framework providing at least the services we had in the past with CERNLIB was necessary before moving to higher level applications. ROOT really means the “roots” for end-user applications. Once we have the roots well installed in the ground, Trees or other Flowers can flourish. We hope that we are reaching this stage now.

A possible acronym for the system could be: “Rapid Object-Oriented Technology”

To learn more on the early history of ROOT, check out the 1997 webpagehttps://cern.ch/root1997mainpage) and this talk at the 2025 ROOT Users Workshop, as well as this nice map.

Just like trees and plants, applications need strong roots to grow and flower. ROOT is a comprehensive object oriented framework that provides a solid foundation on which large scale data analysis applications can be built.