A pending order (or limit order) is an order placed in the system aimed to execute into a position once your selected target rate or better is reached.
An order will be executed if the current market rate of an instrument reaches the selected target rate and it can be executed within a range from this rate depending on market movements and volatility.
These type of orders will stay opened until they get executed or you decide to close them.
For more details regarding the Order Tab, please click here.