The lonsdale falls between other sizes: it is longer than a corona and thinner than a Churchill or a toro. Traditional size charts put it at about 6½ × 42, although actual sizes vary from factory to factory.
Because the ring gauge is thin, the wrapper has a noticeable effect on the flavor. The extra length gives the flavor time to change as the cigar burns down. It suits people who like a parejo that is not thick.
According to traditional accounts, the size was named after the Earl of Lonsdale. The connection is historical and has nothing to do with how the cigar tastes.