Markup and margin both describe profit, but against different bases — and confusing them is a classic pricing mistake. The same dollar of profit is a smaller number as a margin than as a markup.
Two views of the same profit
Margin is profit as a share of the selling price; markup is profit as a share of the cost. A product that costs $60 and sells for $100 has a $40 profit — a 40% margin but a 66.7% markup. Knowing which one a supplier or report means keeps your pricing consistent.