Xvnc versus X11vnc

What is the difference between Xvnc and X11vnc?

Xvnc: Is an X and VNC server at the same time. It is mainly used to run the X server on a virtual display, (in the absence of a physical one) and connect remotely to it with a VNC client/viewer.

X11vnc: Is a vncserver that “publishes” an existing physical X display over VNC, allowing remote clients to connect with it using a VNC viewer. That is, they can see the actual running desktop windows, as if they were in front of the server.