You can find most popular coin collecting phrases in this coin glossary.
oddity - when something unusual happens to a coin it is sometimes called an oddity. Can be an "error" that was made at the mint, or something that was done to a coin after the minting of the coin.
obsolete - a coin design or series that is no longer being produced.
obverse - the front side of a coin. Usually the obverse side of a coin has the main design, date and sometimes mintmark. The back of the coin is called the reverse.
off center - describes the way a coin was struck by the printing dies. If the coin was not placed properly and the dies strike it off center then parts of the design will be missing from the coin. Sometimes an off-center coin will have part of the blank planchlet showing.
original roll - a group of coins that were wrapped in paper wrappers at the time of their production. In early days coins were shipped to banks in cloth bags or kegs. Sometimes later they were shipped in rolls. Silver coins stored in rolls will often have toning on and near the edges but not in the center. Some coins stored in rolls will have fewer marks than those stored or transported in bags or kegs. The number of coins in a roll may vary by denomination and time of issuance. Typically there are 50 cents in a roll, 40 nickels, 50 dimes, 40 quarters, 20 halves, 20 silver and Eisenhower dollars, and sometimes 25 SBA or Sacajewea dollars.
ounce - form of measuring weight. The troy ounce that is used for weighing precious metals is different from the regular grocery store ounce.
over strike - a coin that instead of being struck on a blank planchlet was accidentally struck on a previously struck coin.