Flux can refer to numerous things:

• In physics, especially in fluid mechanics and electromagnetism, flux is the rate at which something flows through a given cross section (vis. a surface). See also rate of fluid flow, magnetic flux.
• In metallurgy and electronics, a flux is a material that acts as a catalyst for smelting and soldering.
• Flow, in psychology, is often referred to as flux.
• Flux is a book by Stephen Baxter.
• A Flux capacitor is a fictional device, a critical component in the time machine in the Back to the Future film and its sequels.