B: A model is a group of elements, such as metadata and source files, that typically constitute a distributable software solution and includes customizations of an existing solution.
D: A model is a design-time concept, for example a warehouse management model or a project accounting model.
E: A package is a deployment and compilation unit of one or more models.
Reference:
https://docs.microsoft.com/en-us/dynamics365/fin-ops-core/dev-itpro/dev-tools/models