The term "stiffer" is an adjective that describes something which has become more rigid or firm. It can be used to describe a material, such as metal or wood, that has been made stronger and less flexible through processes like heat treating or chemical treatment. The word can also refer to a person's posture or movements becoming more upright or rigid due to age, injury or illness. In addition, "stiffer" can be used in the context of suspension systems on vehicles, where stiffer springs and dampers make for a firmer ride.