A lot of newbies to this site don't understand some of the abbreviations used on this board. Here are a few off the top of my head. Feel free to add others or PM (message)

me and I'll add them to the list.
ETA.....Edited to add. Used to tell why a person has gone back and changed a post.
ITT......In This Thread.
OP.......Original Post or Original Poster. Used when a thread has gotten long or off
track and one wants to refer to the original intent of the thread.
IMO......In My Opinion
MHO.....My Honest Opinion (there are many variations on this one)
JMO......Just My Opinion
JMHO Just my honest opinion.
ISC.......I Stand Corrected
IDK.......I Don't Know
FTR.......For The Record
FWIW...For What Its Worth
QFT......Quoted For Truth
OIC......Oh, I see.
NSFW...Not Safe For Work. (naughty, naughty)
PM........Private or Personal Message.
TU........ Temporarily Unavailable. This shows as a members status if they are placed in "TU" for not following the rules. The amount of time a person remains in TU is up to the moderators. During TU, the member is able to read the threads, but can not post in them.
Names are often abbreviated so if you see one you might just have to back up and read to see if there is a name that fits the abbreviation ex...BMO=BlackMoonsOwl, EBS= EarthboundSpirit, FW=Firewillow, LPB= Lilpnkbnny, TPG =The Pet Goddess, H=Hjolmaer, etc...
I know these seem obvious but I see it asked often what these stand for.
ETA....To add useful abbreviations from this thread to the OP per request. If I missed any, let me know.