The Harry Potter book series by J. K. Rowlings is similar to the Lord of the Rings, in that it's read by fairly young children, teens, and adults. The language is advanced enough for adults, which means that some of it is fairly difficult for younger readers.
Sayre Van Young has been a reference librarian for more than 30 years, which has obviously given her the background to pick and choose the words that need to be defined for readers to get the most out of the books. Considering that J.K. Rowlings has professed a commitment to education, I've been surprised that she has not created or at least approved more educational books and workbooks based on her series. This vocabulary builder, or as I think of it, extensive glossary on Harry Potter is a wonderful addition to the bookshelves of Harry Potter fans.
Ms. Young doesn't bother to "define" Ms. Rowlings fabricated vocabulary, such as "muggles," instead she combed all seven books and chose 3000 of the most difficult vocabulary words to define. Some of the vocabulary is British in nature, and therefore the explanations will be very welcome by American Harry Potter fans.
It's interesting to note that as Ms. Young wrote her definitions, she ended up creating a set of characters that reappear throughout the book. If you're curious about them, check out the epilogue.
The Unofficial Harry Potter Vocabulary Builder is an essential companion book for any young, and even not so young, readers who are working on the seven book Harry Potter series. Think you don't need it? Define volauvents.