Give a definition

Yes, there are other terms that are needed to be defined first which are:

Plane: A plane is a flat surface on which geometric figures are drawn.

Point: A point is a dimensionless dot which is drawn on a plane surface.

Line: A line is collection of n number of points which can extend in both the directions and has only one dimension.

Now,

(i) Parallel lines: When two or more lines do not intersect each other in a plane and perpendicular distance between them ramains constant then they are said to be parallel lines.

(ii) Perpendicular lines: When two lines intersect each other making a right angle in a plane then they are said to be perpendicular to each other.

(iii) Line segment: A line segment is a part of a line with two end points and cannot be extended further. It has a definite length or breadth.

(iv) Radius of circle: The fixed distance between the centre and the circumference of the circle is called radius of the circle.

(v) Square: A square is a quadrilateral in which all the four sides are equal and each internal angle is a right angle.