A managed package is a container that includes the components of a Salesforce application, and it’s a mechanism for installing apps in Salesforce orgs.
Important This topic only applies to Government Cloud customers, whose apps still use the legacy connected apps framework. The majority of Mobile Publisher
customers, whose apps use the external client apps
framework, don't need to request, install, or maintain managed packages to use Mobile Publisher.
After you have a draft of the Android and iOS versions of your Mobile Publisher app, it’s time to request a managed package. Salesforce creates a managed package for each Android and iOS app. A managed package is required for the Mobile Publisher app to function correctly.
The managed package includes components that help your app run properly. For example, push notifications won’t work unless you install the Mobile Publisher managed package in your Salesforce licensed orgs.