Terraform is a a platform used for doing "Infrastructure as Code" - IaC. It's created by the company HashiCorp, and is a opensource project available here on Github.

With IaC, you're creating your infrastructure - either on-premise or in a cloud - with code. By doing that, you're sure fx both your dev, QA and production are created the same way. When you're learning to handle IaC, it will also be faster to create new servers or systems. (But there is a learning curve :) ).