Puppy eyeliner is a makeup technique that creates a downward curve at the outer edge of the eye, giving the eyes a more rounded, "puppy dog" appearance. It is essentially an inverted cat-eye look, where the eyeliner goes down instead of up and out. This technique is particularly useful for people with hooded eyes or a fold over their lid, as it can help avoid distortion caused by a winged eyeliner interfering with the fold.

To achieve the puppy eyeliner look, one can follow these general steps:

1. Tight-line the upper waterlines with a creamy brown liner to define the eyes.
2. Starting at the center of the lids by the lashes, draw a thin line downward following the natural slope of the eyes.
3. Fill in the eyeliner towards the center of the eyes with the same brown pencil along the lower lashes.
4. Use a small brush to smooth out the edges.

Puppy eyeliner is a popular makeup trend that originated in K-Beauty and has gained popularity worldwide. It is a sweet and cute alternative to a traditional sexy cat-eye, and can make the eyes appear larger and rounder by following the natural downward slope of the eyes.