"Margin" means a difference. Forex Margin trading means that one trades currencies backed by a fractional deposit of money (the deposit serves as collateral to your account). The margin is measured in percentages from the total value of the position, for example a 1% margin of a $1,000,000 USD/JPY position is $10,000. What this means is that in order for somebody to buy $1,000,000 of USD/JPY one would need to put down $10,000 or 1% margin.