flux

This term is defined in ECSS-E-ST-10-04C as
amount of radiation crossing a surface per unit of time, often expressed in “integral form” as particles per unit area per unit time (e.g. electrons cm-2s-1) above a certain threshold energy

This term is defined in ECSS-E-ST-10-12C as
number of particles crossing a sphere of unit cross-sectional area (i.e. of radius 1/ ) per unit time

This term is defined in ECSS-Q-ST-70-06C as
amount of radiation crossing a surface per unit of time

This term is defined in ECSS-Q-ST-70-08C as
material which, during soldering, removes the oxide film, protects the surface from oxidation, and permits the solder to wet the surfaces to be joined