What is Infrastructure
The layer applications run on: cloud servers, networks, and deployment systems, and the engineers who build and run it.
In plain terms
Infrastructure engineers own the foundation under the product: setting up cloud resources, keeping services online, and automating deployment. Their tools are distinctive on a resume: Kubernetes, Terraform, Docker, Ansible, Helm, and one of the major clouds.
What it tells you about a developer
Infrastructure skill develops by running real systems at scale, so it is a strong seniority signal on its own. These engineers are scarce and senior-skewed, so expect outbound sourcing to carry the search. Someone who owns infra can usually write competent backend code as well.
Related
Read the lesson on Infrastructure More in How software gets built