obligation

Information given in the lettered inscriptions on the back of a note, describing its exchangeability. As an example, certain early Legal Tender Notes have this inscription: “This note is a legal tender for all debts, public and private, except duties on imports and interest on the public debt, and is receivable in payment of all loans made to the United States.” Also called Legal Tender Status.

obsidional coins

Emergency coins struck during battle, also called siege pieces.

obverse

The front or face side of a coin, generally the side with the date and principal design.

OGP

Original government packaging.

overdate

A date created by superimposing one or more numerals on a previously dated die.

overgraded

A coin in poorer condition than stated.

overstrike

An impression made with new dies on a previously struck coin.

overvalued

A coin whose legal-tender exchange value has been set at a rate higher than its face or intrinsic value in an effort to discourage its export.

oxidation

The formation of unsightly discolored spots of areas on a coin as a result of exposure to humidity, air pollutants, or other environmental factors.