In software deployment, an environment or tier is a computer system or set of systems in which a computer program or software component is deployed and executed. In simple cases, such as developing and immediately executing a program on the same machine, there may be a single environment, but in industrial use, the development environment (where changes are originally made) and production environment (what end users use) are separated, often with several stages in between. This structured release management process allows phased deployment (rollout), testing, and rollback in case of problems.