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 subdirectories spanning downward.
The root node of a file system is also called the root directory. On a Windows-based PC, "C:\" represents the root directory of the C drive. On Macintosh and Unix systems, the root directory is designated by a simple forward slash ("/"). Similarly, the root directory of a website is simply the domain name, followed by a forward slash (i.e. http://www.techterms.com/). If you ever use a terminal program to view files and folders on a computer, you can use the command "cd /" (change directory to root) to navigate to the root directory.
"Root" is also the name of the user who has administrative privleges on a Unix or Linux server. While most users can only access data within their own directory (i.e. "/users/~fred/"), the root user can access any folder on the hard drive. This allows the root user to install system software updates, modify the access privileges of other users, and perform other administrative tasks.