A provider is a doctor or hospital. Networks are the doctors or hospitals contracted with an insurer to participate in a given insurance product. Insurers increasingly sell plans with smaller networks, meaning they exclude many doctors and hospitals from their plans, because that's cheaper. But there are limits to how narrow a network can get because there are network adequacy rules to ensure that insurers actually have in-network providers who deliver the services covered by the insurer. Trump's rules make it easier to narrow networks even further. And raise deductibles higher.