Like all collectibles, the rare coin market has its own terms and slang. The following is a brief definition and explanation of the most frequently used coin collecting terms.

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impaired Proof

A Proof coin that grades less than PR-60; a circulated Proof.
See Also --   mishandled Proof

incandescent light

Direct light from a lamp, as opposed to indirect light such as that from a fluorescent bulb.

incomplete strike

A coin that is missing design detail because of a problem during the striking process. The incompleteness may be due to insufficient striking pressure or improperly spaced dies.

incuse design

The intaglio design used on Indian Head quarter eagles and half eagles. These coins were struck from dies which had fields recessed, so that the devices – the areas usually raised – were recessed on the coins themselves. This was an experiment to try to deter counterfeiting and improve wearing quality.

Indian cent

Common name for an Indian Head cent.

Indian Head cent

Those James Longacre design cents struck from 1859 until 1909. From 1859 until mid-1864, these were composed of copper-nickel alloy, while those struck mid-1864 to 1909 were struck in bronze.

Indian Head eagle

The Saint-Gaudens designed ten-dollar gold coin struck from 1907 until 1933.

Indian penny

Slang for an Indian Head cent.

Intrinsic value

The value of the metal(s) contained in a numismatic item. The United States issues contained their intrinsic value in metal until 1933 for gold coins and 1964 for silver coins. Today’s “sandwich” coins are termed fiat currency.

investor

An individual who buys numismatic items strictly for profit, not caring to complete a set or particular collection.

iridescence

A "glow" displayed by a coin, often gleaming through light pastel colors.