My Yu-Gi-Oh card says it inflicts Piercing damage what does this mean?

Answer 1

A card that can inflict "Pierce" Damage means that it is able to inflict excess ATK points onto your opponent if it can successfully attack a Defense Position monster your opponent controls whose DEF is lower than the attacking card's ATK. In the TCG, cards that have a "Piercing" effect are categorized by having the effect text:

"During battle between this attacking card and a Defense Position monster whose DEF is lower than the ATK of this card, inflict the difference as Battle Damage to your opponent."

For example, Player A's Dark Driceratops (ATK: 2400) attacks Player B's Defense Position Mystical Elf (DEF: 2000). Regardless if Mystical Elf is destroyed or not, Player B takes the difference (400 points in this case) as damage.

In one instance, the card Cyberdark Horn had the effect printed as "This card inflicts Piercing Damage" instead of the above text as a means to introduce new terminology to the TCG public as "Piercing Damage" is a term used in the OCG. However, this did not catch on and Konami decided not to push this any further.