The Rembrandt triangle is a concept you use to get beautiful shadows and highlights on a person’s face. It all relates back to the painter, Rembrandt, and his paintings.  They all have strong highlights on one side and shadow on the other. The strong side angled light creates a little triangle shadow next to the nose. Some consider this to be the Rembrandt triangle, some consider a small triangle of light on the cheekbone on the shadowed side of the face to be the Rembrandt triangle.

Two other shots I took.