PL/SQL User's Guide and Reference
APPENDIX E. Reserved Words
The words listed in this appendix are reserved by PL/SQL; that is, they have a special syntactic meaning to PL/SQL. So, you should not use them to name program objects such as constants, variables, or cursors. Also, some of these words (marked by an asterisk) are reserved by SQL. So, you should not use them to name database objects such as columns, tables, or indexes.