Redstone Flux, often referred to as RF, is the central energy system in Team CoFH's mods and various others. RF is often used to power machines or tools.
So what is so useful about an energy system? As an example, take a look at Minecraft's own Furnace. The Furnace uses fuel like coal to smelt items. One piece of fuel lets the Furnace smelt a certain amount of items. However, if there aren't any more items to smelt while a piece of fuel still is being burnt, the remaining energy in the piece of fuel will be wasted! An energy system like Redstone Flux solves problems like that. The potential power that a piece of fuel contains can be converted to a certain amount of RF. This RF can then be consumed at a much more precise rate, saving any fuel that is left.
Check out 'Redstone Flux: A Primer' for a more in-depth introduction to how Redstone Flux works.
There are four kinds of things that can be done with Redstone Flux:
Redstone Flux can be produced by certain devices. These devices usually consume some kind of fuel to do so, or convert other types of energy into RF.
Some examples of devices that generate RF:
Redstone Flux can be moved by various means. Usually this involves pipe-like blocks that carry RF around or blocks that can teleport RF.
Some examples of devices that move RF:
Redstone Flux can be stored by some blocks and items. Some devices are dedicated to storing RF, and some have an internal buffer for their operations.
Some examples of devices that store RF:
Redstone Flux can be consumed by devices that perform specific actions. Machines and powered tools do this instead of the primitive way of consuming pieces of raw fuel.
Some examples of devices that consume RF: