Data package is a single compressed file that contains a data project manifest and data files. This is generated from a data job and used for import or export of multiple files with the manifest.
Integration can be used where the real-time, service-based integration is needed, or when you need an asynchronous integration.
Pushing data from staging to target: From staging, the data is moved to the target by using the data entities that have been defined. This move can be done either in a row-by-row manner or by using a set-based manner, if the data entity supports it.
Data project is used to store configuration, default processing options, and mapping definition.
A data entity allows the data to be exposed outside of Dynamics 365. Without a data entity, the data cannot be accessed in a Power App.