1 [mass noun] the action or process of flowing or flowing out:the flux of ions across the membrane Physics the rate of flow of a fluid, radiant energy, or particles across a given area. the amount of radiation or particles incident on an area in a given time. the total electric or magnetic field passing through a surface. 2 Medicine an abnormal discharge of blood or other matter from or within the body.
(usually the flux
) archaic diarrhoea or dysentery.
3 [mass noun] continuous change:the whole political system is in a state of flux
4a substance mixed with a solid to lower its melting point, used especially in soldering and brazing metals or to promote vitrification in glass or ceramics. a substance added to a furnace during metal-smelting or glass-making which combines with impurities to form slag.
treat (a metal object) with a flux to promote melting.