A Plan must be understood as an item, granting a certain level of access (e.g.: Bronze, Silver, Gold or Platinium), associated to a set of entitlements (e.g.: HD, 4K, family - 4 simultaneous streams for a SVOD service). If the Plan is a renewing subscription, it is associated to a renewal periodicity.
The purpose of the Plan is to aggregate a same in-app item, distributed over various Mobile Applications Store, into a same object, with a shared identifier, that you can define yourself. This contributes to simplify the follow-up of your subscribers.