By now most you may have heard the term “Product Backlog” in Agile terminology. You can consider this term to be referring to our erstwhile vocabulary of requirements documents with a slight twist.
The point about managing requirements in Agile is that you can use any tool available to manage what is needed to build the product. It could be a wiki, it could be jIRA, it could be Rally or even an excel sheet. The means to detail requirements do not matter. What matters is how the requirements are listed, when they are ready for design and execution, when and where they are discussed with teams and how they are made more and more clearer as time progresses. We need to maintain this essence while handling the requirements.
So coming back to product backlog – think of it as a list of requirements to build a product with two important considerations: the priority to develop a listed item, and the clarity available to implement a listed item. Priority obviously means what is more important to do (even in normal life). Clarity available means what is actually Ready.