Added glossary

docs/articles/monetization-glossary.md

@@ -2,3 +2,30 @@
 title: Monetization Glossary
 sidebar_label: Glossary
 ---
+
+This document contains a list of concepts and terms that are useful to
+understand regarding Zuplo's monetization product.
+
+## Stripe Subscription
+
+Subscriptions in Stripe are what register a user to the Product they have
+purchased. When a user goes through the checkout process, they will be
+registered as a Customer in Stripe with a Subscription. The Subscription will
+contain a single Stripe Product.
+
+## Stripe Product
+
+A Stripe product is where the price of your API Plans are specified. Stripe
+handles the billing, currency exchange rates, tax calculations, etc. Products in
+Stripe match with API Plans.
+
+## API Plan
+
+An API Plan is where you specify the quotas that will be enforced for a
+particular user that has purchased access to your API. Plans contain a field
+(`External ID`) that is used to reference a Strip Product.
+
+## Metering Service
+
+The Zuplo Metering Service is the service that stores the "API Plan" data and
+keeps track of the meters that are consumed within your API.