What is Margin?

Legal Definition
1. The edge or border; the edge of a body of water where it meets the land. As applied to a boundary line of land, the "margin" of a river, creek or other water-course means the center of the stream. Ex parte Jennings, 6 Cow. (N. Y.) 527, 16 Am. Dec. 447; Varick v. Smith, 9 Paige (N. Y.) 551. But in the case of a lake, bay or nainral pond, the "margin" means the line where land and water meet. Fowler v. Vree-land, 44 N. J. Eq. 268, 14 Atl. 116; Lem-beck v. Andrews, 47 Ohio St. 336, 24 N. E. 686, 8 L. R. A. 578.

2. A sum of money, or its equivalent, placed in the hands of a stockbroker by the principal or person on whose account the purchase is to be made, as a security to the former against losses to which he may be exposed by a subsequent depression in the market value of the stock. Markham v. Jau-don, 49 Barb. (N. Y.) 468; Sheehy v. Shinn, 103 Cal. 325, 37 Pan. 393 ; Memphis Brokerage Ass'n v. Cullen. 11 Lea (Tenn.) 77; For-tenbury v. State, 47 Ark. 188, 1 S. W. 58.
-- Black's Law Dictionary
Legal Definition
A deposit by a buyer in stocks with a seller as security to cover fluctuations in the market. See 192 Pa. 304, 73 Am. St. Rep. 812, 43 Atl. 793.
-- Ballentine's Law Dictionary