"Skin is a port" .... means the skin is not your own work...entirely or in part, being derived from the work of another, not necessarily limited to the Windowblinds section.  Eg, many Winamp skins are 'ported' from Windowblind skins and vise versa.  Shell themes are done similarly.

Normally this is a very complex process as there is no simple mechanism for achieving good results....much manual detail work is needed.

Complex or simple...all ports require consent from the original artist prior to upload/public distribution...