How do you define the relationship between product marketing and demand generation within your organization?

Not clear on this question... do you mean "describe" instead of "define"?

The relationship between product marketing and demand gen is symbiotic. And at my organization thankfully the relationships is highly collaborative.

It wasn't always this way. When I led product & customer marketing, I should have set a better example for the PMM team by synching with the head of demand gen more frequently and voicing my concerns more aggressively. Why should PMMs be more tightly connected to demand gen marketers when their manager wasn't?

In any team or organization, there has to be push/pull between individuals to get the most out of one another. PMM needs Demand Gen to scale programs while running experiments to ensure continuous product-market fit, while Demand Gen needs PMM to iterate on messaging and collateral to diversify hooks that either capture or create demand.