= O =
Ob-
Obfuscated C Contest
obi-wan error
Objectionable-C
obscure
octal forty
off the trolley
off-by-one error
offline
ogg
old fart
Old Testament
one-banana problem
one-line fix
one-liner wars
ooblick
op
open
Open DeathTrap
open switch
operating system
optical diff
optical grep
optimism
Orange Book
oriental food
orphan
orphaned i-node
orthogonal
OS
OS/2
out-of-band
overflow bit
overflow pdl
overrun
overrun screw