Mark-up refers to the percentage increase or simply increase OVER the cost incurred in a product. It is in contrast to Mark-Down which is a discount offered on the selling price.
Eg. Rs 8 is the cost of a CHIPS PACKET, and the producer wants a 25 % mark up, the mark-up price would be
Rs8 + 25% of Rs 8
i.e, Rs 8 + Rs 2=Rs 10
Hence the chips would reach the retailer at Rs 10 Mark-up.