Let's start by recalling how we can construct the polar coordinate system in a plane. To do this, we need to fix a point O that will represent the origin of the polar coordinate system. Then, we can construct an initial ray from point O called the polar axis. That ray would look like the following diagram.
Then, each point P in the plane can be assigned polar coordinates (r, θ), where r is the directed distance from O to P, and θ is the directed angle, counterclockwise from the polar axis to segment OP.
Recall that the origin of the polar coordinate system is also called the pole. With this in mind, let's complete the sentence.
The origin of the polar coordinate system is called the pole.
