What is a variety, die or hub

Definition: A hub is a positive, or relief (raised) image of the coin which has been impressed into a steel die during the process of creating coin dies. The original coin image is actually a plaster sculpture about 8 to 12 inches in diameter, from which a Master Hub is created using a special process that reduces the image to actual coin size. This Master Hub, which bears a relief image of the coin design, is then copied into a select number of Master Dies, (which bear the negative, or incuse image of the coin.)
The advent of modern minting technology has enabled the production of huge volumes of virtually identical coins. They are struck on high speed presses using tools called dies. Each die is a negative image of the coin it is intended to produce. The dies are in turn produced by being impressed by a tool called a hub which contains the features of one side of the coin it is designed to manufacture. The hubbing process is used to make dies of a consistent quality. Within a given year's production, slight but noticeable differences may occur in the die making process. Coins struck from these dies are known as varieties.
For some great information on the process of die production, check out the Comprehensive Encyclopedia (The "VAM" book by A. George Mallis and Leroy Van Allen).
While these dies are from a Counterfeiting ring in Thailand, the image shows what a working die would look like.

Variety
There seems to be some confusion as to exactly what constitutes a variety. In United States numismatics, a variety may be defined as a die or die pairing that offers some distinctive feature not a normal part of the design. For early U. S. coins, those made before the introduction of the reducing lathe in 1836, every die required extensive hand punching of letters, numerals and other small features. Therefore, each and every die was distinctive, and each die pairing constitutes a variety.
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