A Plan is what a Subscription subscribe to in a monthly subscription type business model. A Plan has a monthly amount that will be charged every month after a Subscription was activated. A Plan also has other fields such as a name and a picture which can be used for displaying on a website or e-commerce checkout flow. A Plan can optionally also be linked to one or multiple Products, which means that those Products will be immediately activated for the Subscription if someone signs up for a Plan. This way you can compile product bundles that can be sold together, such as a "Living Room Plan" for a furniture or audio installation subscription.