I had asked the same to Deepak Alur. Here is his reply
When we first published the Value Object pattern in 2000, we were following the usage of that term in the J2EE community. Subsequently, we realized based on our discussion with leaders in the OO community, that the term Value Object holds a different meaning established years before its usage in J2EE.
The following URLs offer more description of the term Value Object:
http://c2.com/cgi/wiki?ValueObject
http://wiki.cs.uiuc.edu/cs497rej/Value+Object
http://www.martinfowler.com/eaaCatalog/valueObject.html
http://www.martinfowler.com/ap2/valueObject.html