Xuefei ZHANG

Product Marketing Manager is kind of the role project management for marketing & internal communications.  

the PM & PMM are the two core role of product-market/customer bi-directionel communication. 

As PM, the direction is more of external(market/customer) to internal - to study the market needs & trends, to learn about what caters for the clients; whereas the PMM on the contrary - to translate the product info in marketer's way while keeping aligned with the market or customer needs. 

Personally, these 2 roles in binominal collaboration can be combined in some not-too-granulared structures.