1) A terminal server is a specialized computer which aggregates multiple communication channels together. Because these channels are bidirectional, two models emerge: Multiple entities connecting to a single resource, and a single entity connecting to multiple resources. Both of these models are widely used. Both physical and virtual resources can be provided through a terminal server: centralized computing can provide multiple users access to a remote visual operating system. Access Providers often use terminal servers to terminate physical connections to their customers, for example customers who get Internet through some form of modem.
2)Terminal Services is a component of Microsoft Windows operating systems (both client and server versions) that allows a user to access applications or data stored on a remote computer over a network connection. Terminal Services is Microsoft's take on server centric computing.
Based on the Remote Desktop Protocol (RDP), Terminal Services was first introduced in Windows NT 4.0 Terminal Server Edition. The products Windows 2000 Server, Windows 2000 Advanced Server, Windows 2000 Datacenter Server and Windows Server 2003 have introduced several improvements and new features. Microsoft used Terminal Services in Windows XP to allow a user to assist another user (Remote Assistance) and to allow a user to take control of his/her computer remotely (Remote Desktop). Remote Assistance works in all editions of Windows XP, while Remote Desktop requires Windows XP Professional or Windows XP Media Center Edition 2005 or later.
Microsoft provides the client software Remote Desktop Connection (formerly called Terminal Services Client), available for most 32-bit versions of their Windows operating systems and Apple's Mac OS X, that allows a user to connect to a server running Terminal Services. Third-party developers have created client software for other platforms, including the open source rdesktop client for common Unix platforms. Both Terminal Services and Remote Desktop Protocol use TCP port 3389 by default, which is editable in the Windows registry.