Infrastructure As Code is the practice of keeping infrastructure definitions within code and subsequently in version control.
One of the best ways to understand the definition of Infrastructure As Code is to consider the anti-thesis:
Manually created infrastructure is the infrastructure that has been created by an individual, and rather than documented in code it’s documented in textual format, or worse not at all.

Cloud-native applications are more than just the code – today’s applications include infrastructure as code that (IaC) for fast, repeatable deployments.
The 2021 IaC Report:
Infrastructure as Code Security Insights
