Margin represents a security deposit which is at least required to open a trade. In plain terms, margin is the amount you are contributing to a certain trade and in essence it is also the amount you stand to lose should the markets move against you. Margin is also the term used for the amount of money that you need to keep in your account to sustain a position, called the maintenance margin.

Eventually, if your position threatens to wipe your account clean, there will be a point where the position will be automatically closed, this is called a margin stop-out. In order to sustain your positions open, the automatic closing of your position could be prevented by depositing more funds or by closing some of the open positions in order to increase the margin.