The Site root is the file system analog to the Site URL and defines the top-level directory into which Movable Type will publish it's static files and subdirectory hierarchy for the blog.

Example:

/home/melody/public/blog

An absolute path like the one above is strongly encouraged, but a relative path (e.g. "../" meaning one directory up in the hierarchy) is supported and is relative to the Movable Type directory.

This is a required field and is set initially when a new blog is created.