What characterizes a spot transaction in foreign exchange?

A spot transaction in foreign exchange is characterized by the immediate exchange of currencies at an agreed-upon rate. In a spot transaction, parties typically agree on the current market exchange rate for the currencies being traded, and settlement occurs within a short time frame, often within two business days. This immediacy is a key feature that distinguishes spot transactions from other types of transactions, such as forward transactions, where the exchange rate is determined today but the exchange occurs at a future date.

The other options describe different scenarios or concepts in finance. A future date rate agreed upon by two parties refers to a forward contract, where the exchange will occur at a specified future date, not immediately. A commodity exchange involving multiple currencies implies a broader market activity not limited to the direct currency exchange of a spot transaction. Lastly, a reversible transaction that can be altered suggests a level of flexibility usually not associated with spot transactions, as these are generally fixed once agreed upon. Thus, the defining characteristic of a spot transaction is the immediate nature of the currency exchange at an agreed rate.