d - The small letter "d" (pronounced penny) next to the number representing the price of a stamp, is the value in old money that the stamp cost when new. There were 240 old pennies to the pound, but a pound in the old days was worth a lot more than now. For more information, ask old folk, who will go on about this at some considerable length, and will tell you stories which sound as if they are exaggerating, but they're not.