Client Access Licenses: Connecting to a RDS Server also requires licenses in the form of Per User or Per Device Client Access Licenses, this is what allows more than a single user to remote into the server.

If you want to install Office on a RDS Server you will need the Volume License version, or you wont be able to install it Application Licensing: Not any application can be installed on a Remote Desktop Server.If you are looking to save money and already have old machines, you should look at the recently launched OS from Microsoft called Windows Thin PC, which essentially turns your machines into thin clients. The user can remote into the server using the Remote Desktop Connection Manager included in Windows or more often than not can connect from thin clients, in fact they can connect from anything that implements the Remote Desktop Protocol. All you applications are installed once and available for any user to run. You can think of it as a computer that lots of people remote desktop into at the same time, however they all have there own user session and desktop, and are completely unaware of each other. RDS, as it is abbreviated, allows you to have a powerful server that all your users connect to using the Remote Desktop Protocol (RDP). Starting with Server 2008 R2, Terminal Services has been renamed to Remote Desktop Services. What is Terminal Services (Remote Desktop Services)

Windows terminal services