Internet Relay Chat is an open protocol that facilitates plain text chat. Multiple separate networks exist, each with a theme or purpose, each effectively independent from the others. The first version began operation in 1988 and it is still in broad but overall declining use.
Because IRC is an open protocol, there are many different clients that can connect to an IRC network. Any person or organization that wants functionality not present in an existing client is free to implement their own. Clients exist in the form of desktop apps, web apps, mobile apps, and CLI programs, many of which are cross platform.
The primary interaction mode on IRC involves users, often anonymous or pseudonymous, joining one or more channels. Messages sent to a channel are relayed to all other users in the channel, to whom they will appear in chronological order in a view specific to that channel.
Channels are owned and controlled by the first user to join or create the channel, and others selected by them, the channel "ops" (operators). Some IRC networks supply additional functionality for managing channel ownership, and additional rules about which channels can be created and by whom. Ops can kick out or ban individual users or all users matching certain criteria, prohibit sending messages to the channel except from specific users, and change other practical channel configuration.
Servers and Networks
Each user connects to a single server to interact with the network that server is itself connected to. All users on a network can interact with each other as if connected to the same server, unless a "netsplit" occurs where a network connection failure between servers causes one network to break in half, with each half of the split perceiving itself to be the whole network. Different networks running different versions of the IRCd (daemon) software handle synchronization after a netsplit differently.