Seasonal plates (Saisonkennzeichen) are vehicle registration plates that only let you drive during certain months. For example, a motorcycle can have Saisonkennzeichen from April to October, or March to November. You can choose the dates when you register the vehicle.
The main benefit of seasonal plates is that your vehicle insurance is cheaper. You only pay insurance for the months you can drive.
Outside of the allowed months, you can’t drive your vehicle, and you can’t park it on the street.1 You must put it in storage, or use a private parking space.