Remote Desktop Session Host (RDSH) is a role in Remote Desktop Services (RDS), which was known as or Terminal Services prior to Windows Server 2008 R2. RDSH servers host Windows applications or desktops that are accessed by remote users over a network connection.
The benefits of delivering Windows desktops or applications through RDSH instead of installing apps on employees' devices include quicker update roll-outs and the ability for end users to access corporate apps and desktops remotely, using devices that wouldn't normally support those apps or Windows.
Multiple end users can connect to the RDSH server through a Remote Desktop Connection Broker or RemoteApp to access session-based desktops, published applications and server resources. Multiple RDSH servers can be grouped together in a Session Collection and publish either RemoteApp applications or session-based desktops, but not both from the same collection. The ability to group RDSH servers into collections was new to Windows Server 2012 RDS; the feature is useful for load balancing connections between connected servers.
Each remote session on a RDSH server needs a client access license (CAL). The Licensing role in RDS keeps track of those CALs so there aren't more active sessions than licenses. Standard Windows Server licenses include the basic requirements for setting up and using RDSH and licensing services.