Capped range
A range is capped when the way it was played has ruled out the strongest hands, so there is a ceiling on how good it can be.
Ranges get capped by actions, not by cards. A player who only called before the flop and only checked the flop has told you they are unlikely to hold the best possible hands, because those would usually have raised somewhere along the way.
The value of spotting it is that you can bet larger than your own hand deserves. Against a range with a ceiling, a big bet threatens hands that the opponent simply cannot have, and that pressure is available whether or not you hold anything.
an example
your cards
board
Your opponent called before the flop from the big blind and checked this flop. Almost every ace and every pair of nines would have played differently at some point, so their range is capped, and a large bet asks a hand that cannot beat an ace to prove otherwise.
This example is made up. The real one is in your own hand history: find capped range in your own hands and see how often it came up and what it cost you.
related terms
Range
A range is the whole set of hands a player could hold in a given situation, rather than a guess at the one hand they act ...
Polarized
A range is polarized when it consists of very strong hands and bluffs with almost nothing in between, which is the shape ...
Overbet
An overbet is a bet larger than the pot, which asks the opponent for a worse price than any normal size and therefore ne ...
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Knowing the word is not the same as seeing it.
Forty hands against a bot, no account, and your own hand history at the end.