UNION docs

I't unnI don't understand this:

The UNION operator specifies a table derived from a Cartesian product.
The two tables that represent the direct operands of the UNION must
have the same number of columns, and corresponding columns must be
of compatible data types.</para>

Why do you call it a cartesian product. I thought a cartesian product
was tableA x tableB, while UNION is really tableA + tableB, right?

If I am right, can you change the docs? I will leave it as is. Thanks.

-- 
  Bruce Momjian                        |  http://www.op.net/~candle
  maillist@candle.pha.pa.us            |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026