Subdirectory Definition Computers store data in a series of directories. Each directory, or folder, may contain files or other directories. If a directory is located within another directory, it is called a subdirectory (or subfolder) of that folder. Subdirectories may refer to folders located directly within a folder, as well as folders that are stored in other folders within a folder. For example, the main directory of a file system is the root directory. Therefore, all other folders are ...