i)Parallel lines: Two lines in a plane are said to be parallel, if they have no point in common.
In figure, x and y are said to be parallel because they have no point in common and we write, x||y . Here, the term point is undefined.
ii)Perpendicular lines: Two lines in a plane are said to be perpendicular, if they intersect each other at a right angle.
In figure, P and Q are said to be perpendicular lines because they intersect each other at \(90^\circ\).
iii)Line segment: The definite length between two points is called the line segment. ln figure, the definite length between A and B is line segment and represented by AB.
iv)Radius of a circle: The distance from the centre to a point on the circle is called the radius of the circle. ln the adjoining figure OA is the radius.
v)Square: A square can be defined as a rectangle having same length and breadth.