Linear range
A linear range, also called merged or condensed, takes the best hands in a range from the top down with no bluffs, so it bets small hoping to get called by worse.
A linear range takes a player's hands from the very best down to some cutoff point, with no bluffs mixed in. Because every hand in it has genuine value and nothing is included purely to fold out an opponent, a linear range wants to bet small and often, keeping the price low enough that the second-best hands in the opponent's range are happy to call.
Worked example. You raised preflop and the flop comes king high. Your betting range is every king, every big pair, and some strong second pairs, with no air included. Betting big here would only fold out the second-best hands you want to keep in, so instead you bet small, around a third of the pot, and let those weaker hands pay you off street after street.
Solvers reach for this shape when one side has a clear range advantage and does not need bluffs to make betting profitable on its own.