Frankfort horizontal plane

noun

Frank·​fort hor·​i·​zon·​tal plane ˈfraŋk-fərt-ˌhȯr-ə-ˈzänt-ᵊl-, -ˌhär- 

: a plane used in craniometry that is determined the highest point on the upper margin of the opening of each external auditory canal and the low point on the lower margin of the left orbit and that is used to orient a human skull or head usually so that the plane is horizontal

called also eye-ear plane, Frankfort horizontal, Frankfort plane