Multiple environments are necessary during ERP implementations. An ERP implementation usually involve at least three environments, though additional environments might be added depending on implementation project requirements. DEV, TEST, and PROD, are the most common names for these three environments

PROD (May also be called GOLD)

After implementation, PROD refers to the live ERP environment. Prior to implementation, this is a transaction-less environment where tested configurations are setup. Transaction-less because ERP systems don’t have a “delete posted transactions” button, so you want to keep this environment clean from test transactions. So where does transaction testing happen?

TEST (May also be called UAT for User Acceptance Testing)

During the implementation, subject matter experts and end-users will setup sample configurations and model business processes with test transactions in the TEST environment. The desired, approved configurations will then be setup in the PROD (GOLD) environment.

DEV (Mostly just called DEV)

DEV environments are necessary as ERP projects frequently require customizations. A developer can build and deploy his developments to the DEV environment without interrupting the flow of user testing. Once any technical bugs are smoothed out, the customized code from the DEV environment can be promoted to the TEST environment, where it will be validated/approved by subject matter experts or other functional users.

Occasionally in the ERP implementation process, users will want to test/confirm the PROD (GOLD) configurations. To do this, a copy of the data (configurations) in PROD will be refreshed into the TEST environment. At the same time, it is also common to take a copy of the previous data (transactional data and configurations) in TEST and push that to the DEV environment. This users to reference the data and configurations that used to be in TEST if they encounter any unexpected issues while conducting new transactions in TEST (which would indicate configurations needed to be updated in PROD.

In summary:
Data and configurations move from PROD > TEST > DEV while
Development (customizations) move from DEV > TEST > PROD

Use User Options to Distinguish Environments

As a functional consultant, to avoid confusing DEV, TEST, and PROD, I adjust the user options in each to distinguish the environments.

In D365, the user options are under the settings gear in the top right.

DEV

TEST

PROD

Pink for PROD is especially eye-catching.
Has saved me for than once from making a boo-boo.