Forever Order is an order you place in Dhan and wait for it to execute based on the conditions you have entered. Currenlty it is availabe on buy/sell side for Equity & buy side for F&O through OCO

Forever Order is essentially a trigger order that is placed and maintained in Dhan and when the set price is reached your order is sent to the exchange for execution. 

For example, if a stock is currently priced at Rs. 150, then you can place a forever order to buy the stock when the price reaches Rs. 100 in Dhan. So when stock reaches Rs. 100, then the order is triggered and sent to the stock exchange for execution - either at Market Price or Limit price. 

You may refer the link for more details :  Forever Order