reduce

Reduce is a verb with multiple related meanings across different fields. In everyday use, it means to make something smaller, lower, or less in amount, size, or degree.

In programming, reduce (also called fold) is a higher-order function that aggregates a collection into a single value by applying a binary function to an accumulator and each element. It is often contrasted with map and filter; for example, reducing a list of numbers with addition yields a sum.

In chemistry, reduction denotes the gain of electrons in a redox reaction, paired with oxidation. A reducing agent donates electrons, causing another species to be reduced.

In environmental policy and waste management, reduce is the first of the three Rs: reduce, reuse, recycle. It targets lowering resource use, energy consumption, and waste through efficiency, design changes, and mindful consumer choices.

In theoretical computer science and mathematics, a reduction is a formal transformation that shows one problem can be solved using a solution to another problem. Reductions underpin concepts of decidability and computational complexity, and they are used to relate different problems in algorithmic analysis.