Screen Sharing is a VNC

Virtual Network Computing

In computing, Virtual Network Computing is a graphical desktop sharing system that uses the RFB protocol to remotely control another computer...

 client

Client (computing)

A client is an application or system that accesses a service made available by a server. The server is often on another computer system, in which case the client accesses the service by way of a network....

 by Apple Inc. included as part of Mac OS X v10.5

Mac OS X v10.5

Mac OS X Leopard is the sixth major release of Mac OS X, Apple's desktop and server operating system for Macintosh computers. Leopard was released on 26 October 2007 as the successor of Tiger , and is available in two variants: a desktop version suitable for personal computers, and a...

. It allows remote observance or control of any Macintosh machine on the local network that has Screen Sharing activated. It may also be used over the Internet via iChat

IChat

iChat is an instant messaging software application developed by Apple Inc. exclusively for its Mac OS X operating system. It has audio, video and screen-sharing capabilities as well as text messaging...

. Because Screen Sharing is a VNC client, it may also be used to control any computer running a VNC server

Server (computing)

In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...

 if the IP address

IP address

An Internet Protocol address is a numerical label assigned to each device participating in a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing...

 of the target computer is known and accessible. Apple's Back to My Mac

Back to My Mac

Back to My Mac is a feature introduced with Mac OS X 10.5 Leopard that uses Wide-Area Bonjour to securely discover services across the Internet and automatically configure ad hoc, on-demand, point-to-point encrypted connections between computers using IPSec...

 feature of MobileMe

MobileMe

MobileMe was a subscription-based collection of online services and software offered by Apple Inc. Originally launched on January 5, 2000, as iTools, a free collection of Internet-based services for users of Mac OS 9, Apple relaunched it as .Mac on July 17, 2002, when it became a paid subscription...

 service offers Wide-Area Bonjour

Bonjour (software)

In computing, Bonjour is Apple Inc.'s trade name for its implementation of Zeroconf, a group of technologies that includes service discovery, address assignment, and name resolution...

to allow Screen Sharing and File Sharing access beyond LAN.