Stacks[1] are basically recipes for deploying Postgres for specific use cases. This includes extensions, Postgres configs and application deployments (example: PostgREST)

For examples, you can look at https://github.com/tembo-io/tembo/tree/main/tembo-operator/s...

[1] Blog about Stacks: https://tembo.io/blog/tembo-stacks-intro/