IntelliJ IDEA enables using numerous run/debug configurations. Each run/debug configuration represents a named set of run/debug startup properties. When you perform run, debug, or test operations with IntelliJ IDEA, you always start a process based on one of the existing configurations using its parameters.
IntelliJ IDEA comes with a number of run/debug configuration types for the various running, debugging and testing issues. The user can create his/her own run/debug configurations of specific types.
Each run/debug configuration type has its own default settings. Whenever a new run/debug configuration is created, it is based on these default settings.
Temporary configurations are marked with semi-transparent icons and are managed same way as
the permanent configurations.
By default, 5 temporary configurations are allowed per project. You can change this limit via the Edit Configurations dialog.
Permanent configurationA configuration of this type is explicitly created for a particular class or method. If there is no permanent configuration for an item, IntelliJ IDEA automatically creates a temporary configuration for it, when you choose or on the context menu of this class or method.
Default vs custom run/debug configurations
When you change the default run/debug configurations, you thus change the settings that will become applicable to any run/debug configuration of the corresponding type created later. Changing defaults does not affect the existing run/debug configurations.
The process of editing the default run-debug configurations is described here. The process of creating or editing the custom run-debug configurations is described on the page Creating or Editing Run/Debug configurations.