Each user or device accessing a licensed Windows Server requires a Windows Server CAL or a Windows Server and a Remote Desktop Services (RDS) CAL.

With the User CAL, you purchase a CAL for every user who accesses the server to use services such as file storage or printing, regardless of the number of devices they use for that access.

With a Device CAL, you purchase a CAL for every device that accesses your server, regardless of the number of users who use that device to access the server.

Windows Server 2012 Remote Desktop RDS 50 User CAL