Which term describes a testing environment that separates untested code from the production environment?

The term that describes a testing environment which separates untested code from the production environment is the staging environment. A staging environment is specifically designed to replicate the production environment closely, allowing developers to test new features and changes in an environment that mimics the real-world usage without affecting actual users or live data. This helps to identify any potential issues before code is moved into production, ensuring that any bugs or flaws can be addressed first.

In this context, while quality assurance refers to the overall process and practices aimed at ensuring that the software meets certain standards, it does not specifically describe the environment used for testing the code prior to deployment. The development environment is where developers build and initially test their code but does not necessarily provide the security and fidelity to the production environment that a staging environment does. An isolation environment typically refers to a broadly defined area set up to prevent interference and enhance security, but it is not a commonly used term for a specified testing stage like staging is. Thus, the staging environment stands out as the most accurate descriptor for the scenario described in the question.