Definition: A key date is a coin that is usually the last to be placed in a collection, because the date or date and mint mark combination is especially rare or hard to find. It is the coin that most collectors need to complete a certain collection.
See a list of the Wheat Penny Key Dates.
See a list of the Wheat Penny Key Dates.
Examples:
His collection of Lincoln Cents would be complete if he could just find that elusive key date, the 1909-S VDB penny.