ssRNA -ve viruses: segmented vs unsegmented

[IAN DWORKIN]

 I am doing some research on  filoviruses and mononegaviridae in general, I have come across the term segmented vs unsegmented , however my virology text has n defn for it and have not found any clear meaning for the term segmented. I am guessing that segmented may be for viruses without overlapping genes and unsegmented have overlapping genes but if anyone in virology land can help me by giving me a definition and some examples I would be very happy.
 I can be reached here or at IDWORKIN at TRENTU.CA

thanks in advance
Ian