default
A value or thing to use when none is specified by the user. Defaults are important for making systems behave in a predictable way without the user having to give lots of "obvious" details.
For example: the default TCP/IP port for the HTTP protocol is 80, the Unix ls command does not list files whose names begin with ".", the default number base in most contexts is 10 (decimal), the default filename extension for Microsoft Word documents is ".doc".