Vortex filament
From Glossary of Meteorology
vortex filament
A line along which an infinite vorticity in a fluid motion is concentrated, the surrounding fluid being free of vorticity.
In an autobarotropic frictionless fluid, a vortex line always consists of the same fluid particles; the vortex filament is, thus, a vortex line and is the limiting case of a vortex tube as the cross- sectional area of the tube shrinks to zero.