What does the term "marked cards" refer to?

The term "marked cards" specifically refers to cards that show wear or distinct differences that can be used to gain an unfair advantage during a game. These could include any noticeable alterations, such as scratches, dents, or other physical traits that differentiate one card from another in a player's deck. This situation can lead to challenges in maintaining a fair game environment, as players may subconsciously or intentionally rely on the markings to identify specific cards during play, which is against the principles of fair play in Magic: The Gathering. Therefore, identifying such cards is vital for judges and players alike to uphold the integrity of the game.