What does it mean if something is 'stiff'?

The term 'stiff' refers to a material or object that is firm or hard, exhibiting resistance to bending or deformation. When something is described as stiff, it implies that there is an inherent rigidity that prevents it from easily changing shape under pressure or force. This property is important in various scientific contexts, especially in materials science and physics, where understanding the stiffness of materials can influence their applications in construction, manufacturing, and engineering.

In contrast to the other options, which describe various properties such as flexibility, softness, and fragility, the defining feature of stiffness is its ability to maintain form and rigidity against external forces. Thus, emphasizing 'firm or hard' accurately aligns the term with its intended meaning in scientific discussions.