Also called markup, margin, gross margin, profit margin
Markup and margin both describe profit on a sale, but against different numbers. Markup divides the profit by what the item cost you. Margin divides the profit by what you sold it for. Both should be worked out before GST, since the tax is not your money.
Mixing them up is one of the most common pricing mistakes. If you want a 25% margin and add 25% to cost, you only get 20%. Over a year of sales, that gap is a lot of money. Always check which one a supplier or a report means before comparing numbers.
An item costs ₹80 and sells for ₹100, before tax. The profit is ₹20. Markup is ₹20 ÷ ₹80, which is 25%. Margin is ₹20 ÷ ₹100, which is 20%. To earn a 25% margin on an ₹80 item, the price has to be ₹80 ÷ 0.75, about ₹107.