Define the official expoansion of "ZODB"

I want to tell people to stop calling it the Zope Object Database.
(Maybe we'll rename it someday, who knows, but in the mean time...)
Bit then I realized that the docs are silent on this, so I decided to
fix this.

doc/index.rst

@@ -201,7 +201,18 @@ Learning more
    reference/index
    articles/index
 
-* `The ZODB Book (in progress) <http://zodb.readthedocs.org/en/latest/>`_ 
+* `The ZODB Book (in progress) <http://zodb.readthedocs.org/en/latest/>`_
+
+What is the expansion of "ZODB"?
+================================
+
+The expansion of "ZODB" is the Z Object Database.  But, of course, we
+usually just use "ZODB".
+
+In the past, it was the Zope Object Database, because it was
+developed at part of the Zope project.  But ZODB doesn't depend on
+Zope in any way and is used my many projects that have nothing to do
+with Zope.
 
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