A co-ordinate is referred to an ordered pair of numbers. The co-ordinate was first introduced by Rene Descartes, a philosopher and mathematician from France in the 17th century. The co-ordinates and plane are also referred as Cartesian Co-ordinates and Cartesian Co-ordinate Plane respectively. The slope of a straight line is referred to as the tangent of the angle which is made by the line with the positive x-axis.

The path that is traced by a moving point, under a certain condition or conditions is known as its locus. In Co-ordinate geometry, equation of a straight line means the mathematical representation of the line. The equation of x-axis is y = 0 and the equation of y-axis is x = 0. If a line passes through the origin making an angle θ with the x-axis, then its equation is y = mx.