Blocker

The blocker refers to a specific card in your hand that reduces the chance of your opponent holding a specific combination.

Blockers help to remove hand combinations from your opponent's likely holdings and allow you to make better decisions based on this additional information. For example, if you are holding the ace of spades on a three-spades board, you know that your opponent won’t have a nut flush since you are holding the ace of that suite, so you can use this information to play aggressively and potentially even move all-in to force him of his hand.

Of course, you should not base your decisions just on this information and should always consider the game flow, your position, range advantage, and other important factors in the hand.Therefore, this concept is more of additional information rather than something you exclusively rely on making huge decisions.