Definition
In poker, a "range" refers to all possible hands a player might have at a given point in the hand, given the actions they have taken. Rather than trying to put an opponent on a single hand, modern poker thinking involves constructing an opponent's range — the full distribution of hands consistent with their betting pattern — and making decisions that are profitable against that entire range.
Ranges are typically visualized as a grid of all 169 possible starting hand combinations in Texas Hold'em, with each cell shaded or colored to indicate how frequently that hand is included. A "polarized range" contains mostly very strong hands and bluffs. A "merged range" or "linear range" contains hands in a more continuous spectrum of strength.
Range-based thinking is fundamental to modern poker and is the framework used by solvers. Players who think in ranges rather than specific hands make significantly better decisions and are much harder to exploit.
Example
After a player 3-bets preflop and bets the flop on A-K-7 rainbow, their range is likely polarized: they probably have very strong hands (AA, KK, AK) or complete air (suited connectors they turned into bluffs), with few medium-strength holdings.