A margin management mode where only some of the available funds are assigned to open trading positions.
An isolated margin is the amount of an available balance that a trader has allocated to an open position. The point of this partial allocation of funds (rather than using all the funds in the available balance) is to guard against potential losses and the forced liquidation of the entire balance. Thus, traders only isolate a part of their funds, gaining some confidence regarding their maximum possible loss in the process.
An isolated margin mode is the safer alternative to a cross marginal mode. In the latter, all the funds in the available balance are distributed across open positions.