What does "margin" mean?

Additional senses

1. 2.(Com.) The difference between the cost and the selling price of an article.
2. 3.Something allowed, or reserved, for that which can not be foreseen or known with certainty.
3. 4.(Brokerage) Collateral security deposited with a broker to secure him from loss on contracts entered into by him on behalf of his principial, as in the speculative buying and selling of stocks, wheat, etc. N. Biddle. Margin draft (Masonry), a smooth cut margin on the face of hammer-dressed ashlar, adjacent to the joints. -- Margin of a course (Arch.), that part of a course, as of slates or shingles, which is not covered by the course immediately above it. See 2d Gauge.
4. 5.To furnish with a margin.
5. 6.To enter in the margin of a page.