It is a cephalometric landmark with significance in biological anthropology and in clinical applications such as oral and maxillofacial surgery.

The Frankfurt plane (also called the auriculo-orbital plane) was established at the World Congress on Anthropology in Frankfurt, Germany in 1884, and decreed as the anatomical position of the human skull for comparative craniometric measurements.

It was decided that a plane passing through the inferior margin of the left orbit (the point called the left orbitale) and the upper margin of each ear canal or external auditory meatus, a point called the porion, was most nearly parallel to the surface of the earth at the position the head is normally carried in the living subject.

In normal subjects, both orbitales and both porions lie in a single plane.

The formal definition specifies only the three points listed above, sufficient to describe a plane in three-dimensional space.