Margin is the selling price of a product minus cost of goods. Using the above example, the margin for a product sold for $200 with a cost of $110 would be $90. Which is a 45% margin (margin divided by selling price).
Markup is the amount by which the cost of a product is increased in order to obtain the selling price. For example a markup of $90 on a product that costs $110 would give a selling price of $200. Which is an 82% markup (markup divided by product cost).