Define the term 'porosity' in relation to hair.

Porosity in relation to hair refers to its ability to absorb moisture. This characteristic is crucial because it affects how well the hair can retain hydration and other products. Hair with high porosity tends to absorb moisture more easily but may also lose it just as quickly, leading to potential dryness. Conversely, hair with low porosity may resist moisture absorption, making it more challenging to achieve proper hydration. Understanding porosity is essential for selecting appropriate hair care products and establishing effective moisture retention strategies, which are vital for maintaining healthy hair.