Mintmark used to signify coins struck at the New Orleans, Louisiana branch Mint.
O number
Overton number describing a particular die marriage for early U.S. half dollars, named for Al C. Overton, who in 1967 authored the book, Early Half Dollar Die Varieties 1794-1836
O-Mint
Term used for the coinage of the branch Mint in New Orleans, Louisiana.
obverse
The front, or heads side, of a coin. Usually the date side.
oct
Short for octagonal (Pan-Pac octagonal commemorative fifty-dollar coin).
off center
A coin struck on a blank that was not properly centered over the anvil, or lower, die. Coins that are 5 percent, or less, off center are graded by PCGS as a regular coin. Those struck off center more than 5 percent are graded as error coins. There will be an “E” before the coin number to designate an error specimen and the amount struck off center will be listed, rounded to the nearest 5 percent.
OMM
Short for "over-mintmark"
open collar
Its name notwithstanding, a closed collar that surrounded the anvil (or lower) die used in striking early U.S. coins on planchets whose edges already had been lettered or reeded. An open collar was a restraining, or positioning, collar that made it easier to position a planchet atop the lower die, and also sometimes kept the planchet from expanding too far.
orange-peel surfaces
The dimple-textured fields seen on many Proof gold coins; their surfaces resemble those of an orange, hence the descriptive term. Some Mint State gold dollars and three-dollar gold coins exhibit this effect to some degree.
original
A term used to describe a coin that never has been dipped or cleaned, or a coin struck from original dies in the year whose date it bears.
original roll
Coins in fixed quantities wrapped in paper and stored at the time of their issuance. The quantities vary by denomination, but typically include 50 one-cent pieces, 40 nickels, 50 dimes, 40 quarters, 20 half dollars and 20 silver dollars. U.S. coins were first shipped to banks in kegs, later in cloth bags, and still later in rolls. Silver and gold coins stored in such rolls often have peripheral toning and untoned centers. Obviously, coins stored in rolls suffered fewer marks than those in kegs or bags.
Original rolls
Rolls of coins that have been together since the day they were removed from their storage bags. Also, rolls of Mint State coins that have never been searched or "picked over."
original toning
Term for the color acquired naturally by a coin that never has never been cleaned or dipped. Original toning ranges from the palest yellow to extremely dark blues, grays, browns, and finally black.
over -mintmark
A coin struck with a die on which one mintmark is engraved over a different mintmark. In rare instances, branch mints returned dies that already had mintmarks punched into them; on occasion, these were then sent to different branch mints and the new mint punched its mintmark over the old one. Examples include the 1938-D/S Buffalo nickel and the 1900-O/CC Morgan dollar.
over dipped
A coin that has become dull from too many baths in a dipping solution.
overdate
A coin struck from a die with a date that has one year punched over a different year. Save a few exceptions, the die overdated is an unused die from a previous year. Sometimes an effort was made to polish away evidence of the previous date. PCGS requires the overdate to be visible to be recognized.