Extensions, rules, and data elements are building blocks. When you want to make your application do something, these building blocks are added to libraries and then a library is "built" into a build. Those builds are delivered to a hosted location.
Adapters define available destinations where the builds can be delivered. For mobile properties, the Managed by Adobe adapter is only available adapter.
Important: This adapter will be used by all environments in a property.
When you create a new property through Adobe Launch, a default adapter of this type is created for you.