This means that excel will use the windows regional settings for that format.
For me, the first sample in that format|cells|number tab|date category|type box
looks like:
*03/14/2001
I use this as my short date format in Windows regional settings: mm/dd/yyyy
(I like leading 0's and a 4 digit year.)
This setting doesn't mean much until the workbook is shared with others. If you
use m/d/yy (no leading 0's and 2 digit years) for that windows setting and
format a cell using that date format, you'd see:
3/14/01
But when I opened that same workbook on my pc, I'd see: 03/14/2001
This can be a problem if the column isn't wide enough to support all those
characters. I may see ####'s. And if you protect the worksheet or I don't know
how to widen the column, it can become a pain.
But if you never open the workbook on another pc (and never change that windows
setting), it won't mean much to you.