We might know the references to “sugar plum fairies” from Tchaikovsky’s Nutcracker Suite and the phrase “ while visions of sugar plums danced in their heads” from Moore’s poem “The Night Before Christmas.” But we probably have not eaten sugar plums.
The name came into general usage in the 1600s. Back then sugar plums were a luxury because it took a laborious process over several days to layer the dried fruits (the word “plum” at one time was used to denote any dried fruit) and nuts and shape them into a small round or oval candies and roll them in sugar. http://en.wikipedia.org/wiki/Sugar_plum
Today recipes abound and if you want to try making contemporary sugar plums, I found this recipe (and the photo) at: http://everydayhealthyeverydaydelicious.com/sugar-plums/