Question

what is polar coordinate

Answer 1

The reference point (analogous to the origin of a Cartesian system) is called the pole, and the ray from the pole in the reference direction is the polar axis. The distance from the pole is called the radial coordinate or radius, and the angle is called the angular coordinate, polar angle, or azimuth.

Answer 2

A pair of coordinates locating the position of a point in a plane.

The first being the length of the strait line (r) connecting to the point of origin.

And the second the angle (theta) made by this line with a fixed line.

Note : refer a figure.

Hope it's useful.

All the best.