I think calling a service/stack (or whatever, app, etc) a "root module" is a very, very confusing thing to do. Terraform has actual micro objects called modules. We work with them every day. I get how you could consider encompassing an entire chunk of terrafrom code that calls various modules a "root module".. but I think this is just going to lead to absolute confusion to anyone not familiar with your terminology. I don't know every TF conversation but I can't think of a single time where I've heard root module in that context. Very good chance I've just missed those conversation and am ignorant to them.

I'm currently hiring SRE 2s and 3s so I've been interviewing lots of terraform writers and one of my tech questions is to ask someone what makes them to decide to write a terraform module and what type of modules they've written - it's always ALBs, EKS, dbs, etc. components indepedently that go into creating a service/stack. I've definitely not heard anyone mention that they write "root modules" in the sense of an entire service/stack.

I don't mean you're right or wrong, maybe more people are aware of that verbage than I am. I just wanted to mention that in my personal case I think it's confusing so I would assume that there are a lot of people in my shoes who would also be confused by it.