Meaning & History. Possibly from the name of the Greek city of Delphi, the site of an oracle of Apollo, which is possibly related to Greek Î´ÎµÎ»ÏÏÏ (delphys) womb. It was used in the play 'The Prophetess' (1647), in which it belongs to the title prophetess. Popularity. See Popularity Detail.
In elementary geometry, the property of being perpendicular (perpendicularity) is the relationship between two lines which meet at a right angle (90 degrees). The property extends to other related geometric objects. A line is said to be perpendicular to another line if the two lines intersect at a right angle. Explicitly, a first line is perpendicular to a second line if (1) the two lines meet; and (2) at the point of intersection the straight angle on one side of the first line is cut by the second line into two congruent angles.
Definition. Parallel lines are two lines that are always the same distance apart and never touch. In order for two lines to be parallel, they must be drawn in the same plane, a perfectly flat surface like a wall or sheet of paper. Parallel lines are useful in understanding the relationships between paths of objects and sides of various shapes.