Edd stands for Easy Data Description, but you might find it easier to think of it as Easy DD. Ok, back to the beginning. DD is a GNU program that lets you write data directly to a disk drive. It has lots of cool and complicated features that are useful to a fraction of people. Edd takes the most useful bits of dd used for when you want to write (typically) an IMG file or ISO to a USB drive, adds a sprinkling of validation and writes it to your chosen USB device. The simplest way to think about this is if you've ever used Unetbootin to write ISOs to CDs/DVDs, well Edd does the same thing but for IMG files.
The main purpose of Edd is to give people who are unfamiliar with Linux an easy (read: GUI) option for writing IMG files to a USB drive. In the future (or even currently) I can see people using USB drives much more than CDs so the ISO medium is kind of dated. We need a tool that is better equiped for writing to USB drives than getting new Linux users to use the command line. Especially when the potential for dd to go disasterously wrong is so high.
Edd fulfills these new requirements by being GUI based, as simple as possible, has ability to support multiple languages and multiple operating systems, unit tests for validation, and includes check to determine if you are going to over-write something important.