At a job ten years ago, I had a manager who thought it would be a good idea to lock us in a meeting room all day with a 45 page BRD reading it line by line and analyzing what each line means until everyone was on the same page.

Every time I do an agile project without a BRD I think of her.

@DutchmanDavid business requirements document. In waterfall projects, pretty common prior to agile, you would get a document that contained every single feature an application needed that would be signed off by all stakeholders. And developers would use that to create the application. No sprints or stories.