Wikipedia
In finance, a forward contract or simply a forward is a non-standardized contract between two parties to buy or to sell an asset at a specified future time at a price agreed upon today, making it a type of derivative instrument. This is in contrast to a spot contract, which is an agreement to buy or sell an asset on its Spot Date, which may vary depending on the instrument, for example most of the FX contracts have Spot Date two business days from today.
Note: the current usage of the term forward is inconsistent. Compared to the trade date, the spot date is already two days ahead in the future. There is no reasonable argument why two days ahead is not forward but three days is forward. An overnight date is before spot date, so consequently it should be called backward. Furthermore, some currency pairs (e.g. CAD and USD) trade spot as only one day after today, etc.
The party agreeing to buy the underlying asset in the future assumes a long position, and the party agreeing to sell the asset in the future assumes a short position. The price agreed upon is called the delivery price, which is equal to the forward price at the time the contract is entered into.
The price of the underlying instrument, in whatever form, is paid before control of the instrument changes. This is one of the many forms of buy/sell orders where the time and date of trade is not the same as the value date where the securities themselves are exchanged.
The forward price of such a contract is commonly contrasted with the spot price, which is the price at which the asset changes hands on the spot date. The difference between the spot and the forward price is the forward premium or forward discount, generally considered in the form of a profit, or loss, by the purchasing party.
Forwards, like other derivative securities, can be used to hedge risk (typically currency or exchange rate risk), as a means of speculation, or to allow a party to take advantage of a quality of the underlying instrument which is time-sensitive.
A closely related contract is a futures contract; they differ in certain respects. Forward contracts are very similar to futures contracts, except they are not exchange-traded, or defined on standardized assets. Forwards also typically have no interim partial settlements or "true-ups" in margin requirements like futures – such that the parties do not exchange additional property securing the party at gain and the entire unrealized gain or loss builds up while the contract is open. However, being traded over the counter (OTC), forward contracts specification can be customized and may include mark-to-market and daily margin calls. Hence, a forward contract arrangement might call for the loss party to pledge collateral or additional collateral to better secure the party at gain. In other words, the terms of the forward contract will determine the collateral calls based upon certain "trigger" events relevant to a particular counterparty such as among other things, credit ratings, value of assets under management or redemptions over a specific time frame, e.g., quarterly, annually, etc.