IRC, or Internet Relay Chat provides a way of communicating with people from all over the world. IRC consists of many networks, which are effectively machines connected up to each other much like your typical home network, except some networks may have machines spread out over many miles.
Users connect to these networks with software known as IRC clients. This software creates an interface for the user to interact with other users, each of whom have a client connected to the same network.
Networks are further divided into channels, which are compared to chat rooms. Each channel usually has it's own topic for discussion, or is about a specific project or piece of software. Converstations on a channel can be public (visible to all in the channel) or private (only visible between you and the user you are talking to). These private conversations are called Private Messages, which is commonly abbreviated to PM.
You can always come talk to us on IRC by visiting us in the #e107 channel on Freenode, which is a service of The Peer-Directed Projects Center (PDPC)
Clients for IRC are purely about user taste. If you ask 10 IRC users what client they think is the best, you will end up with about 5 different answers. Some clients however, are better suited to new users, whereas others are more suited to more experienced users.
mIRC - Probably the most popular windows clients. This client has a 30 day trial. Registration can be purchased for a one time fee of 20.00USD.
HydraIRC - HydraIRC is an open-source IRC client with an attractive and easy to use interface. Donations are always appreciated by the developers.
Xchat - This is an unofficial free X-Chat (UNIX IRC client) build for Windows, compiled on Windows XP SP2 with Microsoft Visual Studio .NET 2003 Enterprise Architect C/C++ compiler.
Chatzilla - ChatZilla is an IRC client that is written entirely in JavaScript and XUL. You must be using a Mozilla based browser to run ChatZilla.
irssi - Easily the most popular linux client. This is a console-only client, none of that GUI stuff to get in the way. Fully perl scriptable and of course it's totally free.
BitchX - Another console only linux client. This client is also very popular, although many avoid it just because of the name and some of the default /part messages it has.
Conversation 2.14 - A great IRC program for mac users.