For nuclear reactions involving the splitting of elements such as Uranium or Plutonium, generally for the purpose of generating power or weaponry. Subclass of the [nuclear] tag, not to be confused with [fusion]
Nuclear power generation or nuclear weaponry driven by splitting of fissile or fissionable materials such as Uranium or Plutonium and other radioactive heavy elements.
There's a small amount of overlap with fusion when it comes to reactions involving lithium or boron, which may split into smaller nuclides during fusion reactions. In general, reserve this tag for reactions involving actinides and similar heavy metals, and use fusion for reactions involving lighter elements.