What term describes the thickness or diameter of the individual hair strand?

The term that describes the thickness or diameter of the individual hair strand is hair texture. Hair texture refers specifically to the quality and coarseness of the hair, which encompasses whether the hair is fine, medium, or coarse. Understanding hair texture is essential for selecting appropriate hair care products and styling techniques, as different textures respond uniquely to treatments and styling methods.

In contrast, hair density relates to the number of hair strands on the scalp, indicating how full or thin the hair appears. Hair porosity refers to the hair's ability to absorb and retain moisture, and hair length simply accounts for how long the strands are from the root to the tip. Each of these other terms serves a distinct purpose in the realm of hair care and styling, but they do not define the thickness of each hair strand.