A 'Game of Thrones' primer on what exactly is a Dunk and Egg

Hello Game of Thrones fans, it's discourse time. 

With rumors that there is another Thrones prequel series in the works at HBO, this time based on George R.R. Martin's tales of Dunk and Egg, many may have questions like "really?" "should we get our hopes up?" and "Dunk and what?" Only some of those questions have answers, but...