Folders can be put together to make a "filesystem" and are laid out like a tree. The folders inside folders are like branches and sub-branches off the tree trunk. This idea is used by the software to allow the user to navigate the folders. A computer file, such as a spreadsheet or music file can only be in one folder directly. This folder, however, can be inside other folders. On some operating systems, shortcuts or links can be made from one folder to another to make it appear that one file or folder is contained in two different parent folders. On Unix systems, this is called a "symbolic link", and is similar in function to a hyperlink.