Flux means constant change or movement. When something is in flux, it keeps shifting and hasn't settled into a fixed state. A river is in constant flux as water flows downstream, never staying the same for even a moment. Your plans might be in flux when you haven't decided whether to go to the park or the movies, and your decision keeps changing based on the weather, your friends' opinions, and your mood.

Scientists use flux to describe the flow of something through a space or across a surface, like the flux of light hitting a solar panel or the flux of heat moving through a window. In this sense, flux measures how much of something passes through over time.

That flowing quality defines the word: flux suggests movement, change, and uncertainty. When a teacher says the classroom seating chart is in flux, she means it's still being adjusted and hasn't been finalized. When historians describe a period of flux, they mean a time when society was changing rapidly and unpredictably. Things in flux often eventually settle, like a snow globe that calms down after being shaken.