Hard link
From Computer History Wiki
A hard link is a connection (one of potentially several) between a file name in a file system and the contents of another (the 'target'; which does have to exist at the time the link is created), such that references to the first name wind up at the file named by the second.
They differ from symbolic links in that if the target file is deleted, and replaced with a different file, references to the hard link will still go to the old file. Only when the last link/name for the old file contents is deleted from the file system do the contents of the old file disappear.
