Why Polar form describes a complex impedance as a vector: a length (magnitude, Z in ohms) and the angle that vector makes with the resistive axis (phase angle, in degrees). It is written as Z angle theta, for example 100 ohms at 30 degrees. The magnitude comes from the square root of R squared plus X squared, and the angle from arctangent of X divided by R.
Watch out Real and imaginary parts, or R and X values, describe the same impedance in rectangular (Cartesian) form; both forms hold the same information, they just use different axes.
Polar = how long and which way (magnitude and angle). Rectangular = how far right and how far up (R and jX).