Better Date - A date (or date and mint mark combination) in a series that is harder to find than general mintage in the same series.

Tough - A date that is more difficult to find due to mintage numbers.

Key Date - Key date refers to a date (or date and mint mark combination) of a given coin series or set that is among the hardest to obtain due to low mintages numbers.

Semi Key Date - Semi key date refers to a date (or date and mint mark combination) of a given coin series or set that is harder to obtain than other more common dates in the series.

Rare - A coin with substantial value based on its low mintage.

Scarce - A coin that is not often seen because of its low mintage.