Which cosmetic product is applied to enhance brows?

The application of an eyebrow pencil or gel is specifically designed to enhance brows. These products serve to define, shape, and fill in eyebrows, allowing for more control in achieving the desired look. The formula used in eyebrow pencils or gels is often designed to match hair color and texture, providing a natural finish. Additionally, these products usually come in various shades to cater to different hair colors and skin tones.

In contrast, the other options do not primarily serve the purpose of enhancing eyebrows. Eyeshadow is typically used on the eyelids to create various eye looks, while lipstick is formulated for the lips to add color. Foundation is meant to provide a base for the skin, evening out skin tone, rather than focusing on facial features like eyebrows. Thus, the eyebrow pencil or gel stands out as the product specifically intended for brow enhancement.