This is a custom dimension of the type "URM category". Here static information on a user can be tracked.
The "-" classifies all users that are not assigned to one of the URM categories.
We cannot provide further information here, as each Category is configured individually in your Mapp Intelligence system.
For further questions please contact your Mapp Intelligence administrator.
Learn more about typical use cases in the training chapter "Setup Options for the Tracking of Elements"