Polygons: – A polygon is a closed curve made up entirely of line segment.
Sides: – It refers to the line segments which form the polygon, as in the above figure AB, BC, CD and DA are its sides.
Vertex: – Point where 2-line segment meet, as in the above figure A, B, C and D are its vertices.
Adjacent sides: – If any 2 sides share a common endpoint, they are said to be adjacent to each other thus called adjacent sides, as in the above figure AB and BC, BC and CD, CD and DA, DA and AB are adjacent sides of polygon.
Adjacent vertices: – It refers to the endpoints of the same side of the polygon. As in the figure A and B, B and C, C and D, D and A are adjacent vertices of the polygon.
Diagonals: – It refers to the joins of the vertices which are not adjacent to each other. As in the above figure AC and BD are diagonals of the polygon.