What is "Key", when Collecting Coins?

Key Coin: A coin that is among the toughest and1921-S would be considered the "keys" and the
Most Expensive to obtain within a series. In the1916-S likely would not, because the 1916-S either
Lincoln Cent series, for example, the 1909-S VDBnot available at all, or is plentiful. Also Key Date
would be considered the key, as would themay be a replaceable term.
1914-D and often the 1922-Plain.Another example, using Lincoln Cents: The "key
A coin somewhat lesser in stature but still amongdates" for the Lincoln Pennies, from 1909 -1958
the tougher in a series to collect is called a(wheat cents) are: 1909s, 1909s VDB, 1914 D,
semi-key; the 1909-S and 1931-S fulfill this role1922, and the 1931 S.
within the Lincoln Cent series for many collectors.The "semi-key" dates are: 1910 S, 1911 D, 1911 S,
The Concept of "Key" may also apply to the1912 S, 1913 D, 1913 S, 1914 S, 1915, 1921 S,
Type or Purpose of the coin collection, rather1922 D, 1923 S, 1924 D, 1926 S, 1931 D, and
than the individual coin. For example, if a collector1933 D.
is putting together a collection of Walking LibertyCertain Sellers use the term "Key Date" to
Half Dollars, without regard to the Condition of thegenerate interest in a coin, whose date may be
coins, then the "keys" are the 1921, 1921-D, and"Key", however, the Condition of the coin is
1916-S.usually less than desirable. Pay Attention!
But, if the Collector is putting together the sameHave fun collecting your Perfect Coins!
set, in Gem BU Condition, the 1919-D and the