The starting point in a hierarchical file system.  In modern operating systems, access to the root directory (root folder) requires administrator privileges (see 
root level).  Gaining access to a file in the hierarchy requires identifying all the directories/folders in the path from the root directory/folder to that file.  In Windows, the command line symbol for the root directory is a backslash (\).  In Unix and Linux, the symbol is a slash (/).  See 
path, 
tree, 
hierarchical file system and 
file system.