VPN is short for Virtual Private Network.
VPN can be used to set up a secure subnetwork via an open, unprotected network (Internet, open WLANs i.e. BayernWLAN) in which communication is protected against interception and access by other participants. This means that the transmission of sensitive data can be as secure as possible against unauthorised access. This is achieved by „tunnelling“ the data traffic via a VPN-gateway/server, to which the connections must be authenticated when they are established, and by simultaneously encrypting the data.
Deutsche Version: VPN Definition