So, what is it, anyway?
Spotted dick is a traditional British pudding made from suet, or mutton fat. The suet is mixed with other ingredients, such as baking soda, flour, molasses, corn syrup, or nutmeg. This creates a pastry dough, to which raisins or dry fruit are added, hence the dessert's "spots." The dough is traditionally either steamed or boiled, and is often served with a custard sauce.
Etymology
Why does such a commonplace, and even appetizing dessert have such a strange, unappetizing name? As mentioned, "spotted" refers to the currants, fruit or raisins in the pastry. "Dick" is messier to explain -- the word itself has a fuzzy history, and in the 19th century alone it was understood as an abbreviation for dictionary, a policeman, an apron, a riding wip, and, of course, male genitalia. Around the same time as these meanings were used, the first recorded spotted dick recipe was created. Etymology resources suggest that the "dick" in "spotted dick" could be "a corruption of the last syllable of pudding," "a corruption of 'dough'," or a reference to the German dick, meaning thick or viscous.