Margin

Margin, often referred to as profit margin, indicates the percentage of the selling price that is profit.

Price = Cost / (1 - % Margin)

e.g., 

Cost = $120.00

Margin = 25%

Price = $120.00 / (1 - 0.25) = $160.00

Markup

Mark-up refers to the amount added to the cost price of a product to determine its selling price:

Price = Cost * (1 + % Margin)

e.g.,

Cost = $120.00

Markup = 25%

Price = $120.00 * (1 + 0.25) = $150.00

Stella specifically uses margin.