An environment is a collection of resources that host the application. Environments typically include host machines and Serena Release Automation agents. When a deployment is run, it is always done so in an environment. While environments are collections of Resources, Resources can vary per environment.
For example, Environment 1 may have a single web server, a single middleware server, and a single database server, that must be deployed to; Serena Release Automation represents these as three, separate resources running in Environment 1. However, Environment 2 may have a cluster of resources to which the same application must be deployed. Serena Release Automation compensates for these differences with resource groups (more at resources by keeping an inventory of everything that is deployed to each environment: Serena Release Automation knows exactly the environment and server(s) where the application was deployed to: and tracks the differences between the environments.