LogFormat "%h %l %u
%t \"%r\" %s %b"
This sets the format of the default logfile named by the TransferLog directive . See the section on Custom Log Formats for details on the format arguments.
If you include a nickname for the format on the directive line, you can use it in other LogFormat and CustomLog directives rather than repeating the entire format string.
A LogFormat directive which defines a nickname does nothing else -- that is, it only defines the nickname, it doesn't actually apply the format and make it the default.