Internet Relay Chat is a old and very popular group communications protocol, developed originally 1988.
It is popular in IRC culture to idle in channels you are interested about, and to stay online 24/7, checking back every now and then if anything interesting has been discussed, you've been addressed etc. IRC channels tend to form around groups of mutual interest or social circle, such as FOSS project channels, friends in a channel, company channels etc. Despite that IRC as an protocol is real time, frequently IRC is not socially realtime as people idle and are not constantly watching the IRC screen. Idling in channels is a very fundamental portion of IRC culture.
For some people private messages without acknowledged permission for such is an insult, generally this kind of people receive a lot of private messages and prefer to have conversations openly in a channel, where everyone may partake. Particularly annoying behavior can be witnessed in mutual interest channels where people come to ask for technical support, a lot of people join, ask their question and within 3 minutes leave, leaving no time for anyone to answer.
New technologies are not really able to challenge IRC due to IRC's nature of simplicity, openness, variety. Newer technologies actually are many times inferior by introducing bloat, client software dependance, unability to operate from anywhere with almost anykind of device which has internet access. Due to IRC's simplicity and low resource demand it is accessible from almost any kind of device with internet access - something more modern chats are simply unable to do due to the sheer bloat introduced.
Some popular clients are:
Bouncers are used for proxying IRC access, and to "virtually" keep you online in IRC all the time.
There are a lot of popular networks, such as: