I am looking for infomation about silk run. Does anyone know exactly what this is? It appears to be something similar to marzipan, but I am not sure.

I've never heard of silk run. I googled it in varying forms and nothing with regard to cake decorating, gum paste, sugarpaste, or marzipan came up.

Perhaps this is what you've heard about:
Sugar Silk Paste by Marcela Sanchez. This very elastic paste is perfect for fine drapes, bows, model clothing, curtains and any elegant super thin decorations.

You can find more at:
http://globalsugarart.com/cat.php?cid=736

HTH
Rae