Rarity n. : The quality or state of being rare; rareness; thinness; as, the rarity (contrasted with the density) of gases.

Rarity n. : That which is rare; an uncommon thing; a thing valued for its scarcity.

Example:
What does the Rarity do to the card value in yugioh?

Taxonomy
rarity, Merriam-Webster Online Dictionary, webster, Webster Online Dictionary with audio pronunciations, dictionary, glossary, english, language.

Defination from the web:
rarity from the Merriam-Webster Online Dictionary with audio pronunciations, thesaurus, Word of the Day, and word games.