You know what it looks like… but what is it called?
TAKE THE QUIZ“flux density”
The following 3 entries include the term flux density.
luminous-flux density
noun: the luminous energy in a beam of light passing a unit normal section per unit time
magnetic flux density
nounradiant-flux density
noun: the radiant energy in a beam of electromagnetic, thermal, or acoustic radiation passing through a unit normal section per unit time
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Merriam-Webster unabridged