When it comes to creating applications, there is a need for multiple environments to support the development process. It typically starts on the developers own computer, then on to an integration environment, a QA testing environment, possibly a UAT (User Acceptance Testing) environment, and then finally production. Depending on your organization, you may have some, none, or all of these different environments.
When it comes to security, the focus is typically on the production environment. This is where the instances that all of the users use are on a daily basis. This has all the “real” data. It is where real credit card numbers or social security numbers may reside. There is a lot of effort put on securing the production environment.