What are polar coordinates?

It is a system of coordinates in Geometry whereby the position of a point, say P, in a plane can be determined with reference to a fixed point called origin, denoted by O, and a predetermined direction represented by a ray OA. The measure of length OP, denoted by r, and the measure of the angle that OP makes with OA, generally denoted by a Greek letter theta, are called polar coordinates of P and, P is called the graph of r and theta. One pair of values of r and theta corresponds to only one point in the plane and one point in the plane corresponds to only one pair of the values of r and theta.