Flux is a simple and ubiquitous concept throughout
physics and
applied mathematics describing the flow of a physical property in space, frequently also with time variation. It is the basis of the field concept in
physics and mathematics. There exist two common usages of the term
flux, each with rigorous mathematical frameworks: For transport phenomena, flux is defined as a vector, whereas in electromagnetism, flux is a scalar quantity, as defined by the surface integral. The terms "
flux", "
current", "
flux density", "
current density", can sometimes be used interchangeably and ambiguously, though the terms used below match those of the contexts in the literature.