Perhaps you mean leverage?
This is a type of credit which your broker applies to the funds in your trading account so that you can open positions which are effectively larger than your funds alone would allow. So if you have £10,000 in your account, your broker might allow you leverage of 30x if you wished to trade EUR/USD for example, meaning that any change in the position from your entry price would be worth 30 x the same change of a £10,000 position alone.
This is good if price goes in your preferred direction but obviously very bad if it does not.