docs(terraform): explain HCL (#10225)

roadmaps/terraform/content/what-is-hcl@Hma2IgatFME8STHPwpeMG.md

@@ -1,5 +1,7 @@
 # What is HCL?
 
+HCL (HashiCorp Configuration Language) is a structured configuration language designed to be easy for people to read and write. Terraform uses HCL in `.tf` files to describe infrastructure through blocks, arguments, and expressions. Terraform configurations are declarative: they describe the desired infrastructure state rather than a sequence of commands to create it.
+
 Visit the following resources to learn more:
 
 - [@official@Syntax - Configuration Language | Terraform](https://developer.hashicorp.com/terraform/language/syntax/configuration)