Combos

Individual combinations of two specific cards. There are six ways to be dealt a given pocket pair, four ways to hold a specific suited hand, and twelve ways to hold a specific unsuited one — sixteen in total for any two different ranks.

Because it turns a vague read into a number. If an opponent's range is aces, kings or ace-king, that is not three equal possibilities: twelve combos of aces and kings against sixteen of ace-king, reduced further by any of those cards on the board or in your hand.

To check whether a call is right. Count the value combos and the bluff combos in the opponent's range, compare the ratio to the price you are being offered, and the decision usually answers itself. Blockers are simply combinatorics applied to your own cards.