Capped range
A range stripped of its strongest hands by its past actions
Definition
A range is capped when its past actions exclude — or heavily thin out — the top of the spectrum. Preflop caps: a flat call from the BB rarely contains AA, KK or AK, which mostly went into the 3-bet range. Postflop caps too: two passive check-calls rarely announce better than one pair — monsters would often have check-raised earlier. Against a capped range, the uncapped side holds a powerful lever: big sizings and overbets. The opponent, deprived of nuts, can only respond with bluff catchers — every large bet puts them to an uncomfortable decision, and none of their hands punishes the aggression. The GTO countermeasure is to never be fully capped: keep a few very strong hands in every line — slowplay a share of your monsters, "protect your checking range". That's the price for keeping your passive lines defensible under pressure.
BB check-calls the K♠9♦4♣ flop, then the 2♥ turn. That line rarely announces better than a decent king: sets would often have check-raised, KK and AA would have 3-bet preflop. On the river her range is capped — the ideal spot for a polarized overbet: her bluff catchers face an impossible choice, and nothing in her range beats the value side.