• Input Variables: These are used to pass dynamic values to Terraform configurations.
• Environment Variables: These are used to set values for Terraform commands or to provide sensitive data.
• Output Variables: These are used to expose values from a Terraform configuration to be used by other configurations or by external systems.

Terraform supports several types of variables:

• String: A single string value.
• Number: A numeric value.
• Bool: A boolean value.
• List: A list of values.
• Map: A key-value pair.
• Object: A collection of named attributes that each have their own type.
• Tuple: A sequence of elements identified by their order and each have their own type.

• Variable Type Constraints: You can specify the type of a variable to enforce that the provided value matches the expected type.
• Using Variables in Configuration: Variables can be accessed using the var keyword.
• Providing Values for Variables: Values for variables can be provided in several ways
• Variable Validation: You can add validation rules to ensure that input values meet certain criteria.
• Sensitive Variables: Sensitive variables are used to store sensitive information like passwords.
• Default Values: Variables can have default values, which are used if no other value is provided.
• Conditional Expressions with Variables: Terraform supports conditional expressions that can be used to assign variable values based on conditions.