What term describes the thickness or density of a hair strand?

The term that describes the thickness or density of a hair strand is hair texture. Hair texture refers to the natural pattern of the hair, which can range from fine and thin to coarse and thick. This characteristic is essential for cosmetologists to consider when determining the right products and treatments for different hair types. Understanding hair texture helps in making informed decisions about styling, cutting, coloring, and overall hair care, as different textures have varying needs and responses to products and techniques.

Other terms in the choices refer to different aspects of hair. For instance, hair porosity refers to the hair's ability to absorb and retain moisture, hair elasticity relates to how much the hair can stretch and return to its original shape without breaking, and hair length simply indicates how long the strands are without indicating their thickness or density.