A Release Note can be described as a report that is published in conjunction with the new version of a product or an update to a product (and sometimes upon release of a new product). The purpose of the notes can be for either internal or external consumers.
Typically, Release Notes should include material such as changes appearing in the latest version of the product, why the changes have been made, how this is going to affect the consumer, and what the consumer might need to do differently. It is integral that the notes communicate the change, even if there is a reduction of some sort to the product as opposed to any additions.