A quadrilateral is a four sided closed plane figure
It is formed by the intersection of four line segments at four distinct points in a same plane.
Quadra means four and lateral means sides.
In the above figure 1, a quadrilateral is formed by the intersection of four line segments AB, BC, CD and DA.
A, B, C and D are four corners of the quadrilateral formed by the intersection of the four straight lines AB, BC, CD and DA.
What do you call the above figure?
A Quadrilateral ABCD.
That is how, a quadrilateral is called by naming its four corners prefixed with the word Quadrilateral, just as we would say ‘Triangle ABC’.
A quadrilateral is a four sided closed figure formed in one same plane.
No two line segments out of the four AB, BC, CD and AD are collinear, i.e. lie on a same straight line.
Note the following terms in a quadrilateral
In the quadrilateral ABDC below, if CD is base, then straight line AE perpendicular to CD is Height or Altitude.