At a right angle, like the perpendicular height of a parallelogram is the height line straight up at a right angle from the bottom.

"Perpendicular" is a description of the relationship between two lines, two planes, or a line and a plane. They are perpendicular if they form right angles (90 degrees) where they cross. -- The little lines in the 'plus' sign ( + ) are perpendicular. -- the fllag-pole is perpendicular to the ground. -- The wall is perpendicular to the floor. -- The door is perpendicular to the floor. -- The door is only perpendicular to the wall when it's wide open. If it's only open a little bit, then it's still perpendicular to the floor, but not to the wall. -- Your legs are perpendicular to the floor when you're standing up.