Margin call is a demand from a broker to a trader to deposit additional funds into their trading account to meet the required margin level. The causes of a margin call may vary, but it often occurs when the trader's account equity falls below the maintenance margin level due to a loss in their open positions.

Margin call can happen in any financial market, such as stocks, commodities, and currencies, where traders use leverage to increase their potential profits. However, it also exposes them to higher risks, and if the market moves against their position, the losses can exceed their account balance, leading to a margin call.

Margin call can be a stressful experience for traders as they may have to deposit additional funds quickly, or their broker may liquidate their positions to recover the losses. To avoid margin calls, traders need to manage their risk properly, use appropriate position sizing, and have a solid trading plan.