Workout and Activity alert

On the Venu 3 I have workout alerts and activity alerts (in German Trainingsalarme and Aktivitätsalarme) according to the manual

I have trouble understanding the difference between the both

I understand that I can select an alert in some activities, e.g. to control my heart rate while running, i set activity alert on heart rate which sends an alert eg when i leave a heart rate zone

But what what is the workout alert?

thanks in advance