Key Coin: A coin that is among the toughest and Most Expensive to obtain within a series. In the Lincoln Cent series, for example, the 1909-S VDB would be considered the key, as would the 1914-D and often the 1922-Plain. A coin somewhat lesser in stature but still among the tougher in a series to collect is called a semi-key; the 1909-S and 1931-S fulfill this role within the Lincoln Cent series for many collectors.
The Concept of "Key" may also apply to the Type or Purpose of the coin collection, rather than the individual coin. For example, if a collector is putting together a collection of Walking Liberty Half Dollars, without regard to the Condition of the coins, then the "keys" are the 1921, 1921-D, and 1916-S.
But if the Collector is putting together the same set in Gem BU Condition, the 1919-D and 1921-S would be considered the "keys" and the 1916-S likely would not. Also Key Date may be a replaceable term.
Certain Sellers use the term "Key Date" to generate interest in a coin, whose date may be "Key", however, the condition of the coin is usually less than desirable. Pay Attention!
Have fun collecting your Perfect Coins!
-- Robert L Taylor, JD
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