Product Managers as Coordinators
In his book, All You Need to Know About the Music Business, Donald S. Passman describes product management and product managers as a coordinating function:
"Product managers are in charge of whipping up all the other departments and getting them to work together. This is to make sure that the product gets pulled forward by a coordinated team of horses, rather than torn apart by horses running in different directions."
This statement is not a definition of product management or product managers by any measure.
The equine metaphor describes the Program Manager role, owned by a generalist who guides the product delivery program and manages all the other corporate functions to work in unison and jointly bring a product to market.
The program manager is a uniquely multi-faceted leadership role that interfaces with diverse corporate functions and leads them without authority.
The program manager role is frequently and erroneously assigned to the product manager, hence the confusion.
For more information, see the Program Manager Is the Product CEO chapter on page 155 in the PMTK Book: Second Edition.