When working with multiple projects, the active project is the project that you can modify or build in RealView Debugger:

You can perform any action on this project. However, you might have to perform actions on other projects that you have opened. RealView Debugger enables you to change the project shown in the Code window title bar, so that you can perform actions on a different project. That is, you can make another project the active project. See Changing the active project for more details.