From QRZ.Com, the Icom handout, and Part 97 Of The FCC Rules -
Ham Radio Glossary - An overview of amateur radio terms.
Offset frequency
Frequency difference between transmit and receive.
OM
"Old Man"; affectionate way to address a fellow ham operator, like saying
"Old Buddy!"
OO
"Official Observer"; a volunteer of the ARRL's Official Observer program
who monitors the airwaves for FCC rules violations. For more information, please see
http://www.arrl.org.
OSC
Oscillator
--- SBBSecho 3.20-Win32
* Origin: The Thunderbolt BBS - Little Rock, Arkansas (1:2320/33)