eBay Feedback is the overall rating that the seller or buyer has acquired throughout their lifetime of using eBay. Everytime a user completes a sale or purchase on eBay the seller or buyer the user is dealing with leaves a message describing their dealings with the user. They can set the message they leave as Positive feedback, Neutral feedback or Negative feedback.
Everytime a eBay user recieves a Positive feedback message they are awarded one point to their eBay feedback score, conversely everytime they recieve a negative feedback message they have one point deducted from their eBay feedback score. A neutral feedback message makes no change to their feedback points.
As eBay auctions are publically available where you are buying or selling items from people you have never met (and are likely to never meet) there is a need to be able to highlight the users that are trustworthy, along with those that are not. Leaving a good descriptive feedback message can help other buyers and sellers steer clear of an eBay user you've had problems with, similarly leaving a message when you've dealt with a good eBay user will let other people know that this user is reliable.
When viewing feedback on eBay the positive feedback and negative feedback are mixed together, making it very difficult to find what messages other people have left when they have had problems. The eBay Feedback Tool solves this problem by just displaying the feedback messages that you choose.