A "perpendicular position" means that something is at a 90-degree angle or right angle to another object or surface. It is like a straight line meeting another straight line at a perfect angle. Full definition
This pose is carried out with legs straight up the wall while rest of the body remains in perpendicular position on the ground. (rishikulyogshala.org)
The soft - top stows away in a space - saving perpendicular position. (indianautosblog.com)
Anyone who has slept with a little one knows that stretched out or perpendicular positions and lots of midnight kicking are common — the more space everyone has, the better night's sleep you'll get. (babble.com)