Day Trader - Speculators who take positions in commodities which are then liquidated prior to the close of the same trading day.
Dealer - An individual or firm that acts as a principal or counterpart to a transaction. Principals take one side of a position, hoping to earn a spread (profit) by closing out the position in a subsequent trade with another party. In contrast, a broker is an individual or firm that acts as an intermediary, putting together buyers and sellers for a fee or commission.
Deficit - A negative balance of trade or payments.
Delivery - An FX trade where both sides make and take actual delivery of the currencies traded.
Depreciation - A fall in the value of a currency due to market forces.
Derivative - A contract that changes in value in relation to the price movements of a related or underlying security, future or other physical instrument. An Option is the most common derivative instrument.
Devaluation - The deliberate downward adjustment of a currency’s price, normally by official announcement.