A "book bomb" is when an author or publisher asks readers to purchase a particular book from Amazon on a specific day. If enough readers cooperate, it pushes the book up in Amazon's rankings, giving it much more exposure than it would get if the same number of copies of the book were purchased over a longer period of time.
To schedule a book bomb, you use facebook, twitter, author newsletter lists, and other social media to get the word out: if you're going to buy this book from Amazon, do it on this date, please.
Sometimes it works, sometimes it doesn't—depends on how connected an author is, how much buzz they can generate, and how internet/media savvy their readership is. Sometimes an author or publisher will offer a reward for participation. Send them proof that you ordered and you're entered to win something cool, like an iPad or Kindle
A reasonable goal is to get the book to move up above 1,000 in Amazon's listing. You've done a great job if it shows up in Amazon's top 100 for it's genre. If you're really successful, it might even move to Amazon's top 100 books overall. If a book hits any these markers, it very likely that it will be picked up in Amazon's marketing and sent out in their promo emails to customers.
Some of you may have participated in the recent Book Bomb for Variant by Robison Wells. If you missed it, that's too bad. Here's what happened...
Coordinated by Larry Correia, the Book Bomb took place on Thursday, November 10th. The day before the bomb, Larry reported, "Last night Variant was at #6,068 overall out of six million some odd books, and #74 in his genre."
By the end of the day on Thursday, Variant was #57 on Amazon's Top 100 Book list, #10 in Teen Fantasy and #7 in Teen Sci-Fi.
I've watched Book Bombs play out before but I've never seen one be quite this successful. This is the power of social media in action! If you want to see the details, visit Larry's blog.