Which of the following activities is classified as barbering?

Barbering is distinctly characterized by activities that focus on the cutting, shaping, and grooming of hair. Shaving and trimming hair falls squarely within this definition, as it involves the use of tools and techniques specifically designed for managing hair, making it a central practice in the barbering profession. This activity is not only about aesthetics but also encompasses the traditional skills that barbers have honed over time.

The other options primarily relate to different areas of beauty and personal care. Applying cosmetics is focused on enhancing facial appearance through makeup, which is outside the scope of barbering. Facial treatments involve skin care, which is more aligned with esthetics rather than barbering. Nail polishing pertains to manicures and pedicures, also outside the barber's realm. Thus, the clear definition of barbering points to shaving and trimming hair as the correct choice.