It's a document that's usually produced by a product management group in a company that outlines (very vague, almost laughably so) the "market requirements" - what users will want/need - for a given feature or set of features.
This is usually handed to developers/designers to come up with a "High Level Design" (HLD) that gives the "how" to the MRD's "what".
It's usually only seen in larger software companies.
It'd be more accurate to say that MRDs are an artifact of waterfall design. Waterfall is out of fashion, and so small companies tend not to use it, but if you're shipping hardware (like Cisco does) it's often more natural than agile.
Given the context, I guess it's some kind of product development order?