Dumbledore’s Army: The Dark Side of the Demob is a tell-all book by Rita Skeeter about Dumbledore’s Army. In this book, published on July 31st 2014, Rita described the imperfections of the Dumbledore’s Army members. She promoted it during the 2014 Quidditch World Cup in her article “Dumbledore’s Army Reunites at the Quidditch World Cup Final“(Pm).
Demob is the abbreviation for demobilization, which means "ceasing military operations or withdrawing troops" (Wikipedia).
The word demob may refer to Dumbledore's army never being part of a military interference, so it would mean a group of ineffective fighters. Also, the word may echo the concept of "the mob", which is "a large crowd of people, especially one that is disorderly and intent on causing trouble or violence" (Oxford English Dictionary).
Note the date on which the book is supposedly published - Harry's (and Jo's) birthday!
From the Web
Writing by J.K. Rowling on Pottermore:
- History of the Quidditch World Cup
- 2014 Quidditch World Cup reports
- 2014 Quidditch World Cup final
- The Daily Prophet
Pottermore enhanced reading experience: Quidditch World Cup
Screenshots of the original Daily Prophet coverage of the 2014 Quidditch World Cup on Pottermore: Imgur archive
Pottermore feature: Dumbledore's Army
Harry Potter Wiki: Dumbledore's Army: The Dark Side of the Demob