Reduction

noun

1. The act, process, or result of reducing.
2. The amount or rate by which something is reduced, e.g. in price.

   "A 5% reduction in robberies"

3. A reaction in which electrons are gained and valence is reduced; often by the removal of oxygen or the addition of hydrogen.
4. The process of rapidly boiling a sauce to concentrate it.
5. The rewriting of an expression into a simpler form.