The sacral triangle on the lower back above the buttocks.
The sacral triangle is a triangle-shaped area at the lower back, over the sacrum, at the small of the back. Its base corner is at the top end of the gluteal cleft (the split of the buttocks), and its top left and right corners are at the Dimples of Venus.
At the sacral triangle, the spinal groove disappears largely or entirely. The sacral triangle exists in both males and females. In females, it forms the lower half of the Rhombus of Michaelis.
In visual art, the sacral triangle is important whenever the lower back of a figure is visible. Its angle indicates the angle of the whole pelvis.