Apology for not being more precise. It is in Z/os system.
Initial catalog: ------- (The RDB name is on the DB2. Typically, it's the name of the server when it was originally built, but it could also be an alias .
This was the description given, but I am unable to find the Alias.
When DB2 is installed, it is given a SubSustemID (SSID) which could be any name (although I have only seen 4 character SSID names). The only 'catalog' I know about is the System Catalog tables (SYSIBM.* tables).
If something is defining an Alias name, it sounds like it is being cataloged on another computer client (or DB2 Connect) to allow access to the z/OS system. That Alias name could be anything the person who has (or will) set it up wants.