Definition of "helicity" in English

noun

1. The quality of being helical.

2. (physics, fluid mechanics, electrodynamics) Any of certain measures of the extent to which vortex lines (in fluid flow) or field lines (in a magnetic or electromagnetic field) kink and twist or link and coil around one another.

3. (physics, quantum mechanics) The quantized spin component of a moving particle along the direction of its motion.

   • 1989, John Taylor, 17: Gauge theories in particle physics, Paul Davies, The New Physics, Cambridge University Press, 1992, 1st Paperback Edition, page 467, To understand this name, note that the helicity is, roughly speaking, the spin in the direction of motion.