Disclaimer: I am working at HashiCorp (now IBM) as part of the Terraform
Core team.
This website is my private blog, so the views and opinions expressed are my own.
Since I am involved in Terraform my opinions can sometimes be (unconsciously)
biased, I hope you enjoy the post anyways.
Stacks is an orchestration layer for Terraform in HCP Terraform. You specify components of your infrastructure (e.g. frontends, backends) and deployments (e.g. development / production). Stacks runs each component / deployment combination as their own Terraform Root Module. Components can be connected, deployments are isolated.
You can find more information in the official blog post and the official documentation.