IRC (Internet Relay Chat) is a protocol for simultaneous communication over an IRC server using an IRC client such as XChat. IRC is used for a wide variety of purposes – for getting technical support, for online clans, internal corporate network for communication in real-time between staff members, and much more.
When you use IRC through an IRC client, you connect to an IRC server. Some popular IRC servers include Freenode which is an IRC network focused on free and open source projects. Every IRC server has IRC channels. These are separate “rooms” usually for discussing different topics or for entirely different projects. For example, on Freenode, a channel called #ubuntu is for the Ubuntu open source operating system whereas #html is for discussions relating to the markup language, HTML. Channels are always prefixed with the hash symbol (#) and all channels prefixed with the hash symbol also refers that it is a network-wide channel that is available on an entire IRC network, such as Freenode.
Whichever IRC client you use, to join a channel when connected to a server, you can execute the following command when you are connected to the server: /join #ubuntu or /join #html. However, IRC clients like XChat allow you to connect to a channel by simply typing in the IRC channel in a dialogue box, negating the need to use the /join channel to join a channel on an IRC network you are connected to. There are many IRC clients available – even for iOS, Windows Phone and Android.
Small list of IRC clients.
On Linux distributions such as Ubuntu, Linux Mint, OpenSUSE and others, there’s XChat, KVIrc, Pidgin (which is also an IM client in general),
On Windows, there is mIRC (not free), Pidgin (which is also an IM client in general), Trillian (which is also an IM client), XChat (although the Windows version is not free – a separate developer has made XChat 2 available for Windows for free – search for “XChat 2 for Windows” – although it’s not up to date by any means). There’s also HexChat which is a based on XChat and is completely free.
Mac OS X
For Mac computers, there’s Colloquy, LimeChat (which is also available in the Mac App Store) and Adium (which is also an IM client).
For iOS, there’s Colloquy and IRC999. Both apps are found in the iOS App Store, however Colloquy is not free.
On Android, you can choose from Andchat, androIRC, DaraIRC, fIRC chat and a few others.
Since Windows Phone 7.5, it is possible to use an IRC client on your Windows Phone. A popular IRC client on Windows Phone is IRC7 and WPirc.