Partial order execution occurs when a counter order at this price has been placed for a smaller amount of assets.

Please wait until another order or orders at your price appear and your order is executed completely.

It is possible to cancel a partially executed order. However, you can cancel the order and only return the unexecuted portion of the order (it will be credited back to your balance).
However, please note that if your order has already been executed, this means that you have entered into an agreement with another user, so you cannot cancel it.