terminology - What's the common name for this GUI element? (left-right box, assignmentbox, relationbox)

You often see the following element to assign objects of a certain type to another object. We call it relationbox, but I can't find anything at all about relationboxes on the internet...
It's such a simple and well known element, there's got to be a well known name!

Here is an example (source: http://community.zimbra.com):

Answer

It seems to be known as Dual Listbox or Dual Multiselect.