Root Definition In the computer world, "root" refers to the top-level directory of a file system. The word is derived from a tree root, since it represents the starting point of a hierarchical tree structure. The folders within the tree represent the branches, while the actual files are considered the leaves. However, unlike a real life tree, a data tree can be visualized upside down, with the root at the top and directories and sub directories spanning downward. The root node of a file ...