C2S or Duo  = Coated 2 Sides, this paper can be printed on both sides;  gsm  = grams per square meter, this is the weight of the paper;  mil    = the thickness of the paper - one mil equals 1/1000 of an inch;  opacity = the higher the opacity, the less the printing shows thru the paper, important for C2S paper;  brightness = the higher the number the brighter the paper is;  sqft  = square foot; special order - generally not stocked in our warehouse, not returnable, please allow 1 to 4 weeks for delivery.  Paper is sold in full package/box quantities only, per sheet and per square foot prices are for reference only.  In case of error, package/roll price is used to calculate invoice.