to_date converts char of CHAR, VARCHAR2, NCHAR, or NVARCHAR2 datatype to a value of DATE datatype. The fmt is a date format specifying the format of char. If you omit fmt, then char must be in the default date format. If fmt is 'J', for Julian, then char must be an integer.
The default date format is determined implicitly by the NLS_TERRITORY initialization parameter, or can be set explicitly by the NLS_DATE_FORMAT parameter.
The 'nlsparam' has the same purpose in this function as in the to_char function for date conversion.
Do not use the to_date function with a DATE value for the char argument. The first two digits of the returned DATE value can differ from the original char, depending on fmt or the default date format.