Activity definition groups are basically just 'containers' that make it possible to bring together a wide range of activity definitions under a common denominator.

You can define activity definition groups in Supporting data > Activity definition groups TSI. Subsequently, you can link maintenance activity definitions from various service plans to these groups on any Activity definitions layout where the Activity definition group reference field is available.

In PPM order generation > PPM profiles, you can link one or more Activity definition groups to a PPM profile. The PPM profile defines the scheduled PPM order generation, with or without clustered activities.

For more information on defining PPM profiles, see PPM profile.