- A plane or flat surface.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
Examples from the Web for planum
The lamina inferior diverges ventrally from the planum terminale anterior to the olfactory eminence.
Posterior to the transition zone between the planum antorbitale and solum nasi the pars facialis is greatly reduced.