IMO=in my opinion
LOL=laugh out loud
ROFL=rolling on the floor, laughing

and so on. Many of these got started 'way back when this thing we type on was the ARPANET, running on 160 baud modems, using teletype machines for IO (input/output). Because of the very limited bandwidth, and the large volume of paper involved (no, I mean *NO*, video monitors most places) there was a huge interest in conserving it, hence the abbreviations. For the same reason, smilies appeared before the internet became the internet, using keyboard characters. <--- that was supposed to be a *real* smiley, made with text. <rant on> IMO, the graphics smilies you see everywhere now-a-days are simply effete, a feeble attempt to claim the reality and heady excitement of those early days of packet-switched, WAN computing, back when we played computer games across the country in text mode, because that was the ONLY mode, but we could do it anywhere! Well, anywhere we could sneak into a lab with a teletype and a node. ;-> <end rant>

WAN=wide area network
ARPA=advanced research (something) agency

(sorry, wetware dropping bits. Used to know the 'P' part like my own name...) :]