Imaginary part

The imaginary part of a complex number $z=x+iy$ is the real coefficient $y$ multiplying $i$, written $\operatorname{Im}(z)$.

In the complex plane it is the vertical coordinate. For a zeta zero, the imaginary part is often described informally as its height, while the Riemann Hypothesis constrains the zero's horizontal, real-part coordinate.

See also: complex number, complex plane, real part, non-trivial zero..