A .tfvars file is used by Terraform, an Infrastructure as Code (IaC) tool, to define variables that can be used within Terraform configurations. These files allow you to externalize variable values, making your Terraform code more modular, reusable, and easier to manage. Instead of hardcoding values directly into your Terraform configuration files (.tf files), you can define them in a .tfvars file and then reference them within your configuration. This separation of concerns improves code readability and maintainability, especially when dealing with complex infrastructure deployments. You can have multiple .tfvars files, each tailored to a specific environment (e.g., development, staging, production). Terraform automatically loads files named terraform.tfvars or terraform.tfvars.json. You can also specify a particular .tfvars file using the -var-file command-line option when running Terraform commands like terraform apply. The file format is typically HCL (HashiCorp Configuration Language) or JSON, allowing for simple key-value pairs or more complex data structures like lists and maps. Using .tfvars files is a best practice for managing sensitive information, as you can exclude them from version control and use environment variables or other secure methods to provide the values.