Leaving your irc client connected to a server and sitting in channels even if you are not at the computer. This allows a group of users to stay in contact even if they are not active all the time.
Many misunderstand this concept and think idling means to stare at an inactive channel for hours on end but it just means leaving your client connected even if you aren't there or are doing other things.
Note: things like the following would not be possible if both users were not idling.
9:56am <user1> so user2 how are the girls?
1:12pm <user2> they are doing great! i just got home.
1:12pm <user1> thats good. tell them hi for me :)
This tactic is when on Twitter someonetags the IDF or another governmental account to troll someone else
comradecommissar1917: This position is flawed for it does not take into account various factors that I will tediously belabor.
for_the_lulz_69: @IDF this person wants to blow up a hospital in Tel Aviv
comradecommissar1917: WTF why did you do that?
for_the_lulz_69: IDFing Someone is funny