Terraform is an open-source Infrastructure as Code (IaC) tool created by HashiCorp. Its primary use is to define and provision infrastructure resources across various cloud providers and services using a declarative configuration language.

Terraform configuration files use the .tf extension. They are written in HashiCorp Configuration Language (HCL), which is a structured configuration language that is both human-readable and machine-friendly.

Terraform state is used to map real-world resources to your configuration, keep track of metadata, and improve performance. It's typically stored in a file named terraform.tfstate in the same directory as your Terraform configuration. For team collaboration, it's often stored remotely in a shared location like an S3 bucket or Terraform Cloud.

Terraform providers are plugins that allow Terraform to interact with various APIs and services. They define and manage resources for specific platforms. Examples include AWS, Azure, Google Cloud, Docker, and Kubernetes providers.

Terraform modules are containers for multiple resources that are used together. They allow you to create reusable components, improve organization, and encapsulate groups of resources. Modules can be called and reused across different Terraform configurations.

Terraform workspaces are separate instances of state data that can be used from the same working directory. They're useful for managing multiple distinct sets of infrastructure resources with the same Terraform configuration, such as development, staging, and production environments.

The three main Terraform commands in the typical workflow are:

1. terraform init: Initializes a Terraform working directory
2. terraform plan: Creates an execution plan, showing what actions Terraform will take
3. terraform apply: Applies the changes required to reach the desired state of the configuration

Input variables in Terraform are defined using the variable block in a .tf file. They can be assigned values through command-line flags, environment variables, or in a terraform.tfvars file. Variables are referenced in configurations using the syntax var.variable_name.

Terraform outputs are a way to extract and display certain values from your Terraform configuration. They are defined using the output block and can include any value computed by your configuration. Outputs are often used to provide information about created resources or to pass data between modules.

A Terraform backend defines where Terraform stores its state data files. Using a remote backend (like S3, Azure Blob Storage, or Terraform Cloud) is important for team collaboration, as it allows multiple team members to access the same state, prevents conflicts, and can provide locking to avoid concurrent state operations.