A Spot Contract is a basic, instant money transfer. Made "on the spot" it uses the current exchange rate.
A Forward Contract is a buy now, transfer later option. When the transfer is ordered the current exchange rate is locked in place for the future transfer.
A Limit Order is a transfer in place that is only triggered when the exchange rate reaches a certain level.
The risk with a Forward Contract and a Limit Order is that the exchange rate could go in the opposite way to that which is desired.