RDP stands for Remote Desktop Connection. It is a way to connect to Windows desktop/server. Default port is 3389. If you use Linux, there are 2 client programs:
1. rdekstop is the old client. Support Windows XP,2000,NT,Windows Server 2012 R2.
2. freerdp resumes the work of rdesktop and support new MS authentication for remote desktop.
To connect to Windows, following is the example:
xfreerdp -u login -p password 192.168.0.5
There are many other options. Just run xfreerdp -h to see them.