Hand Range
The full set of possible hands a player could hold in a given situation, rather than a single guessed hand.
Definition
A hand range is the complete collection of hole-card combinations a player might have, given their actions so far. Skilled players do not try to guess an opponent's exact two cards; instead they reason about the range of hands consistent with how that opponent has bet, called, and raised, and they narrow that range as the hand progresses. Thinking in ranges is more accurate than putting someone on a single hand because it accounts for uncertainty and lets you make decisions based on how your hand or range fares against the whole set of an opponent's likely holdings. Players also think about their own range, aiming to play it in a balanced way so opponents cannot pin them down.
Worked example
An opponent raises from early position, and rather than assuming one specific hand, you assign them a range of strong hands (big pairs and high cards) and fold your marginal holding because it fares poorly against that entire range.
Why it matters
For learners, shifting from 'what hand does he have?' to 'what range does he have?' is the key leap toward thinking like a strong player. For professionals, range construction and range-versus-range analysis underpin virtually all modern strategy, from preflop to river.