An amount beyond the minimum necessary is called the margin. If you sell craft items, you need to build in a profit margin so that you actually make money on the sale. You'll go broke if you sell mittens for $10 that cost you $15 to make.
The blank space around the edges of a sheet of paper — as with the page of a book — that surrounds the text is called the margin. It serves a few purposes: (1) The paper can be bound into a book without covering up the words; (2) If you are a teacher, student, or editor, you can make comments or notes in the margin. (3) If you're bored in class, you can doodle there.