The practice of capturing backlog items as user stories is well-established, to the point that many now consider them indispensable to an Agile way-of-working. In short, a user story is a placeholder for a conversation about a possible requirement. It isn’t so much a requirement specification as a vehicle through which a team can evolve a shared cognizance of scope. A user story can, therefore, be seen as a very practical construct. It allows for an emergent understanding of what the requirements actually are.
An Agile sub-culture has developed around these “stories” and the practices through which they are best managed. For example, user story mapping is a popular technique which has emerged as a discipline in its own right, and there are training courses on how to apply it. Other techniques present lower barriers to entry and usage and are effectively considered part and parcel of the user story lexicon. The most widely adopted of these is arguably the Epic.