Definition of "midline" [midline]

• A medial line, especially the medial line or plane of the body. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "So the midline should be a couple of inches above the eye position of an average adult sitting on that couch."
• "The Chinese air force flies up to five sorties a day up to the "midline" of the Taiwan Strait, creating a strain on Taiwan's air defense posture, made more burdensome by the increasing number of nearly-impossible-to-evade, long-range Russian S-300 anti-aircraft missiles."
• "Your child's incision will extend from the far right to just across the midline of the belly, in a curved line above the navel (along the underside of the rib cage)."