Original: The name "Xfce" originally stood for "XForms Common Environment", but since that time Xfce has been rewritten twice and no longer uses that toolkit.
Simplified: The name "Xfce" originally stood for "XForms Common Environment", but after that Xfce has been rewritten twice and no longer uses that toolkit. The name survived, but it is no longer capitalized as "XFce", but rather as "Xfce".