A directory that is located within another directory. A similar term can be used to describe a folder beneath another folder in a graphical user interface (GUI). Below are some additional examples of subdirectories and a subfolder.
In the above MS-DOS subdirectory example Windows is a subdirectory of the System32 directory.
In the above Linux example, home, user, c, and computerhope are all subdirectories of the public_html directory.
In the above example the Windows folder is a subfolder of the Fonts and System32 folders.