The Jacks of Spades and Hearts are the two suits of jacks known as one-eyed jacks. They are called this because unlike the other two suits of jacks, the Jacks of Spades and Hearts are pictured in profile with only one eye visible to their holder.
One-eyed jacks typically come into play in a game of poker after being identified as wild cards. This means that they can substitute for any other card in the deck to make a better hand. The King of Diamonds is also shown in profile with only one eye being visible and is known as the one-eyed king. The one-eyed jacks and the King of Diamonds are collectively called the one-eyed royals.