Hidden Table

Create table " " (EMPNO NUMBER(3));

Creates a table with 4 spaces as its name.
When you select the list of tables from all_tables, such tables are not visible.

To access such a table use
Select * From " ";

(Remember you need to give exactly the same number of spaces as you gave while creating the table).

This feature can be used to store information that you feel is confidential for you.

For Example :

You might create tables of this kind

2 spaces + "MYTAB" + 1 space + "FILE" + 3 spaces

When you create such a table only you know how to access it (Unless someone is intelligent than you to guess it).