Abbreviations

What do "lol", "lmao" and "IMHO" stand for?
These abbreviations stem from the original Usenet, way back when bandwidth was much more limited, and are generally used to make the plain text of an email, or the textual conversation on IRC, more easily understood in the tone of the original poster - ie, to minimise misunderstandings.

They also allow more content to be portrayed with less typing, which, for beginner IRCers, can be significant (more frequent users tend to, out of self defence, learn to type much much faster... although not necessarily any more accurately.)

"LOL" is an abbreviation for Laugh(ing) Out Loud

"LMAO" is an abbreviation for "Laughing My Arse|Ass Off" (depending on which side of the Atlantic you prefer to spell)
 * See also Rolling On The Floor Laughing, Falling Off My Chair Laughing, & friends.

"IMHO" is an abbreviation for In My Humble Opinion
 * There are also the related In My Not So Humble Opinion, In My Totally Arrogant Opinion, etc.

"BRB" translates as Be Right Back

"AFK" is Away From Keyboard

"FWIW" For What It's Worth

A quick google search will show up a number of pages with these and many other variants. Caution is suggested in use - peppering your missives and proclamations with too many abbreviations will confuse the unwary, and annoy the puissant. Moderation is the key.

Unless, of course, your channel decides to use more.