Used to describe a price 'uplift' applied to the cost of manufacture in order to reach a required sales price. Eg, Cost of manufacture $10, Sales Price $15, then Mark Up is 50% - calculated as a $5 uplift divided by $10 cost = 50% Mark Up. NOT the same as Margin (which is 33%).
Not to be confused with Margin, but always misquoted by people who claim they know the difference but don't! Mark Up is a Cost Plus percentage - it's the amount of 'mark up' that is applied to the manufacturing cost of an item to get it to its Sales Price. Eg, Sales Price $50, Cost $25 - then Mark Up = 100% ie $25 uplift on a $25 cost price.