Select, Update, delete , Insert are the Privileges available on a table. If a user creates a table, he is called as owner of the table. He can grant read Privileges(select) to  any other user in the database.But what is an Read Only table ? how it differs from Select privilege?

If a table is marked as Read Only by DBA , then the table can never be modified by any user with in the database Including the user who has created this table.

The alter table command can now be used to make a table read-only. This allows the DBA to make a table read-only across the database, including the owner of the table.

The following Example illustrates this

Alter table my_table read only;

SQL> delete from my_table;
delete from my_table
 *
ERROR at line 1:
ORA-12081: update operation not allowed on table "SCOTT"."MY_TABLE"

alter table my_table read write;

A new column in the [DBA / ALL / USER]_TABLES view, READ_ONLY, has been added to help you determine if a table is read-write or read-only. Valid values for the READ_ONLY column are YES and NO