According to Facebook
> Production Engineering at Facebook is a hybrid between software and
> systems engineering; it keeps Facebook running smoothly and scaling
> efficiently. The Production Engineering team works within Facebook’s
> product and infrastructure teams to make sure our services are
> reliable and scalable. The team writes code and debugs hard problems
> in live production that impact more than 2 billion people around the
> world. From backend services like our Hadoop data warehouses, to
> frontend services like News Feed, to infrastructure components like
> our caching infrastructure, load balancing and deployment systems, the
> Production Engineering team keeps Facebook running.

as *team works within product and infrastructure* meaning it works between developers and operations.