Angle sum property of Quadrilateral Construction of Quadrilateral (compass)
Before you study about what is a Quadrilateral you are advised to read
What is a Polygon ?
"Quad" means Four, so a polygon which have 4 Angles, 4 Sides and 4 Vertices is known as Quadrilateral.
In the Above diagram :-
Quadrilateral ABCD has
4 Sides - AB, BC, CD and DA
4 Angles - ABC, BCD, CDA and DAB
4 Vertices - A, B, C and D