Update: This deal has ended.

Kindle Unlimited is Amazon's $10 per month subscription service to Kindle books. Amazon is discounting the service if you sign up for a minimum of six months. The six month subscription will only cost you $44.95 compared to $59.94, which is a 25% discount. If you're positive you can go crazy with unlimited books, the two-year subscription is 40% off ($143.86 instead of $239.76).

The service includes access to more than one million titles. The list includes great books like Slaughterhouse Five, The Princess Bride, The Handmaid's Tale, and novels you've always said you read but never actually did like 1984. With your subscription, you can read whatever you want covered under the Unlimited banner for free. You also get access to any available audio books, which has the nifty feature of taking over wherever you stopped reading so you can go from the couch to the car without losing your place.

Unlike some of Amazon's other recent promotions leading up to Prime Day, you don't need to be a new user for this deal. If you're already a Kindle Unlimited member, your automatic payments will be temporarily suspended for the amount of time you purchase at a discount and then will kick back in when the time runs out.

However, Amazon does have some vague language in the terms and conditions that says if you've purchased multiple (it doesn't say how many) prepaid plans like in the form of this discount, you won't be eligible.