What is JAMStack?
For example here I have a Gatsby website that pulls the content from Contentful.
The API part here is Contentful I am using Contentful's API to pull content and render it at build time in my website but since a Gatsby website is a full-blown React App at the end of the day you can call APIs also at runtime like Authentication.
What is not JAMStack?
A monolithic server-run web app that relies on a server technology like Ruby, python or Nodejs. What is also not JAMstack is a website that is baked