Xfce is pronounced “ecks-eff-see-ee”. The name Xfce originally stood for “XForms Common Environment”, but since then Xfce has been rewritten twice and doesn't use the XForms toolkit anymore. The name survived, but it is no longer capitalized as “XFCE” and is no longer an abbreviation for anything (although suggestions have been made, such as “X Freakin' Cool Environment”).