The idea with terraform is you describe your infrastructure as config (data), and terraform keeps track of the state within AWS (or whichever provider). So, as

The idea with terraform is you describe your infrastructure as config (data), and terraform keeps track of the state within AWS (or whichever provider). So, as you change your config, terraform will come up with a plan to move from your present AWS state to the desired AWS state. Terraform allows you to easily express the dependencies in your infrastructure, and also knows about the various dependencies that naturally come with AWS services, which allows it to make better decisions in its planning compared to tools like ansible, chef, etc.