Range
A range is the full set of hands a player could hold in a given situation, each weighted by how likely it is, rather than one specific hand you assign them.
A range is not a guess at your opponent's exact two cards. It is the complete list of hands they could plausibly hold in a spot, with each hand weighted by how often it appears given the action so far. Solvers and strong players think in these terms, because a single hand is just one draw from a much larger picture, and playing well means playing correctly against the whole picture rather than the one hand you feel they have.
Worked example. Say a player opens from under the gun with a range written as AA-QQ, AKs, AKo. That shorthand actually stands for three pocket pairs at 6 combos each, 18 combos in total, plus 4 suited and 12 offsuit combos of AK, another 16. The full range is 34 combos. Some hands, like AA, appear only 6 times; others, like AKo, appear 12 times. The range is that whole weighted set, not any single one of those hands.
Put it to work with the Preflop charts.