You can purchase Campus Participation via the Software Shop. It is a way of allocating the financial resources for the federal contract with Microsoft. It is therefore a participation in the refinancing of the Microsoft licenses that RWTH Aachen University has procured for use in the business sector. The Campus Participation itself is not a license. It entitles the holder to use the Microsoft licenses procured by RWTH Aachen University for official purposes in compliance with the contractual and licensing provisions of the federal agreement. The current term is 4 years (01.05.2021 to 30.04.2025). 

You can find more information in the article Microsoft Campus Teilhabe.