The Free On-line Dictionary of Computing (30 December 2018):

Universal Naming Convention
UNC
Uniform Naming Convention

    (UNC) The type of file system path used in
   Microsoft Windows networking to completely specify a
   directory on a file server.

   The basic format is:

   	\\servername\sharename

   where "servername" is the hostname or IP address of a
   network file server, and "sharename" is the name of a shared
   directory on the server.  This is related to the conventional
   MS-DOS "C:\windows" style of directory name.  E.g.

   	\\server1\dave

   might be set up to point to

   	C:\users\homedirs\dave

   on a server called "server1".

   It is possible to execute a program using this convention
   without having to specifically link a drive, by running:

   \\server\share\directory\program.exe

   The undocumented DOS command, TRUENAME can be used to find
   out the UNC name of a file or directory on a network drive.

   Even Microsoft don't know whether UNC stands for "Universal
   Naming Convention" or "Uniform Naming Convention", both appear
   on their website, sometimes withing the same document, but
   with a preference for "Universal".

   (2008-12-09)