\begin{definition}[Definition:Meridian of Surface of Revolution]
Let $S_C$ be a surface of revolution.
Let its smooth local parametrization be of the form:
:$\map X {t, \theta} = \tuple {\map y t \cos \theta, \map y t \sin \theta, \map x t}$
Then the $t$-coordinate curves $t \mapsto \map X {t, \theta_0}$ are called the '''meridians'''.
\end{definition}