A simultaneous session is more than one but limited to three, sessions of ArcGIS Pro or a Premium App run simultaneously by a named user. ArcGIS Pro and Premium App named users are allowed up to three simultaneous sessions of ArcGIS Pro at anytime, irrespective of running the software online or offline. ArcGIS Enterprise manages the number of simultaneous sessions a user can have. Simultaneous Sessions are software independent, for example up to 3 sessions of ArcGIS Pro, and 3 sessions of a Premium App such as Drone2Map can be used.
Simultaneous sessions differ from concurrent use in that only specified named users can run ArcGIS Pro or a Premium App. In the concurrent use environment, any installation of ArcGIS Desktop, ArcGIS Engine, ArcGIS CityEngine, or ArcGIS Pro can access a concurrent use license if the License Manager is specified.