In a normal auction, the seller starts the auction, the price starts from zero (or a low price), and bidders gradually increase the price... Until there is no one else to increase the price.
A reverse auction may mean two things:
1- A reverse auction may mean an auction organized by the buyer to get the lowest price. In this sense, a reverse auction can be conducted in different ways. For example, sellers may submit their bids in a closed envelop, and the lowest price may win.
2- There is also something called "dutch auction". Dutch auction is also called "reverse auction". In a dutch auctions, the seller organize the auction. And, the seller starts with a very high price. The seller gradually decrease the price, until a buyer accepts the price. If the buyer waits too long, another buyer may buy the product. If the buyer is too impatient, he may end up paying too much. This type of reverse auction is aimed to get the highest possible price in the least amount of time as possible.
A normal auction may take a long time, imagine everyone saying "I pay 100$", "I pay 101$", "I accept 102"$, "I accept to pay 103$" etc... Although the seller can determine rules, like "the increments must be a multiple of 10", it may still take long time to reach a price like "1000$". However, in a dutch type reverse auction, the seller counts down from a high price until he reaches zero... This is relatively faster. In the history it has been used to sell things like flowers, fishes etc...
Some good books that I can recomment about this subject are:
www.amazon.com/gp/product/363864104X
www.amazon.com/gp/product/1463756097
search.barnesandnoble.com/bookSearch/isbnInquiry.asp?isbn=1463756097
www.amazon.com/gp/product/B004PGNF2U
Reverse auctions, in the sense of Dutch Auctions, are also supported on eBay. You can also find information about reverse auctions in the eBay site.
There are a lot of details about reverse auctions, but I hope I have been able to give some introduction.......