Yes, we need to have an idea about the terms like point, line, ray, angle, plane, circle and quadrilateral, etc. before defining the required terms.Definitions of the required terms are given below:(i) Parallel Lines:Two lines l and m in a plane are said to be parallel, if they have no common point and we write them as l ॥ m.(ii) Perpendicular Lines:Two lines p and q lying in the same plane are said to be perpendicular if they form a right angle and we write them as p ⊥ q.(iii) Line Segment:A line segment is a part of line and having a definite length. It has two end-points. In the figure, a line segment is shown having end points A and B. It is written as AB or BA(iv) Radius of a circle :The distance from the centre to a point on the circle is called the radius of the circle. In the figure, P is centre and Q is a point on the circle, then PQ is the radius.(v) Square :A quadrilateral in which all the four angles are right angles and all the four sides are equal is called a square. Given figure, PQRS is a square.