Toroidal and poloidal coordinates

In toroidally confined plasmas, as encountered in magnetic confinement fusion, the toroidal direction is the long way around the torus, the corresponding coordinate being denoted by z in the slab approximation or $\zeta$ or $\phi$ in magnetic coordinates; the poloidal direction is the short way around the torus, the corresponding coordinate being denoted by y in the slab approximation or $\theta$ in magnetic coordinates. (The third direction, normal to the magnetic surfaces is often called the radial direction, denoted by by x in the slab approximation and variously $\psi$, $\chi$ or s in magnetic coordinates.)