As per requests by International and Beginner Members, here's a list of commonly used acronyms.
I know some of you can think of many more, so please, PM me (as in Private Message :) ) to add to the list.:

ACR- Adobe Camera Raw
Av- Aperture Value (as Camera Mode)
BAA- Birds as Art (Arthur Morris' trade name)
BG- Background
BIF- Birds in Flight
BIH- Birds in Habitat
BKGR- Background
BOAS- Birds on a Stick
CA- Chromatic Aberration (purple or green fringe around objects)
CW Rotation- Clockwise Rotation
CCW rotation- Counter Clockwise rotation
CS3- Photoshop version CS3
CSO- Chief Spoonbill Officer
DOF- Depth of Field
EXP- Exposure
EV- Exposure value
EC- Exposure Compensation
FG- Foreground
FF- Fill Flash or Full Frame
FEC- Flash Exposure Compensation
GBH- Great Blue Heron
GTG- Get Together (Reunion)
GND- Graduated Neutral Density (filter)
HA- Head Angle
HDR- High Dynamic Range
HH- Hand Held
HoM- Hand of Man (Avian Gallery)
IAC- In Any Case
IQ- Image Quality
IMO- In my Opinion
IMHO- In my Humble Opinion
IPT- Instructional Photo Tour (as per Arthur Morris' use)
IS- Image Stabilization (Canon Term)
IR- Infrared
LL- Lower Left
LR- Lower Right or Lightroom (software)
LLC- Lower Left Corner
M8T- Mate
M8tess- Matess
NR- Noise reduction
OOF- Out of Focus
OS- Optical Stabilization
OTOH- On the Other Hand
OTT- Over the Top
PS- Photoshop
PM- Private Message (when not time related)
PP- Post Processed
QM- Quick Mask (PS Tool)
RWBB- Red-winged Black Bird
ROT- Rule of thirds ( compositional guideline)
S/H- Shadow/Highlight PS Tool
S/S- Shutter Speed
SW FLA- South West Florida
TC- Tele converter
TFS_ Thanks for sharing
Tv- Time Value- Camera mode for s/s
USM- Unsharp Mask (PS Tool for Sharpening)
UL- Upper Left
UR- Upper Right
URC- Upper Right Corner
VR- Vibration Reduction (Nikon Term)
VWD- Very well done
YAW- You Are Welcome