The default display for the database for date columns is often DD-MON-RR. So Januray 1st, 2021 would display as 01-JAN-21. This is horrible. The time portion of the date is missing from the display (an Oracle date is always composed of at least the century, year, month, day, hour, minute, and second) and the RR format will lead to issues in 2050 which isn’t that far away.
To get your Oracle tools (like sqlplus and rman for example) on your Unix/Linux server to show dates in a better format, the following will help.
export NLS_DATE_FORMAT="YYYY-MM-DD HH24:MI:SS"