Internet Relay Chat is an online chat service; most of its users know it as IRC. You can use it to connect to places like Freenode. Each chat room is a channel starting with '#', for example a #nethack channel. You can use this link if you have an IRC client known to your browser Nethack channel on freenode. IRC servers tend to be case-insensitive, so #nethack and #NetHack are the same channel.
Some IRC networks other than Freenode have #nethack channels, for example IRCNet has one. Channels on different IRC networks are not linked. On most networks, #nethack is empty.
Inheriwiki (inheritance.wikia.com) has some IRC Setup help, with instructions on how to obtain an IRC client, connect to Freenode, and register your nick; if you want to go to #nethack, then substitute 'nethack' for 'inheriwiki'.