SQL> create table test (comment nvarchar2(255));
create table test (comment nvarchar2(255))
                   *
ERROR at line 1:
ORA-00904: : invalid identifier


SQL> create table test ("comment" nvarchar2(255));

Table created.

SQL> select comment from test;
select comment from test
       *
ERROR at line 1:
ORA-00936: missing expression


SQL> select "comment" from test;

no rows selected

SQL>

SQL> select keyword from v$reserved_words where keyword = 'COMMENT';
KEYWORD
------------------------------
COMMENT

1 row selected.