When you export a table, you are guaranteed that the contents of that table will be consistent with the time that the export of that table was started. This means that if you start exporting the table at 12:00 and someone makes changes to the data in the table at 12:05 and your export of this table finishes at 12:10, then the export will not contain any of the changes made between 12:00 and 12:10. You cannot change this behavior with Oracle's export utility.
The CONSISTENT parameter controls whether or not the entire export is consistent, even between tables. If CONSISTENT=N (the default), then the export of a table will be consistent, but changes can occur between tables. If CONSISTENT=Y, then the entire dump file is consistent with the point in time that you started the export. I would suggest setting CONSISTENT=Y whenever exporting.
This was first published in August 2004