Reduction in a general sense means to take of a part of a whole thing or to make it smaller.

'Reduction or reducing may may mean in special

• Reduction (chemistry), the reverse of oxidation, half of a redox reaction, adding of electrons to a molecule, which means reducing the valence
• Reduction (cooking), the process of thickening a liquid mixture such as a sauce by evaporation
• Reduction (philosophy), in philosophy, the process of explaining a particular concept or phenomenon in terms of more fundamental concepts or phenomena
• Reduction (linguistics), in linguistics, the shortening of the pronunciation of a word. e.g. wanna, lemme, gimme.
• Reduction, in physiology, another name for weight loss or dieting
• Reduction (orthopedic surgery), in orthopedic surgery, a medical procedure to restore a fracture to a correct alignment
• Reduction (town), a form of Catholic mission in South America in the 17th and 18th centuries
• Purchasing reduction, in economics and in waste management, is the process of decreasing the purchase of consumer goods
• Reduction (Sweden), in 1680 a return of lands to the Crown earlier granted to the nobility.
• Waste reduction is the first and most desirable component of the waste hierarchy (reduce, reuse, recycle)

In mathematics and computer science:

• Reduction (mathematics), the process of manipulating a series of equations or matrices into a desired 'simpler' format
• Reduction property, in descriptive set theory, a pointclass allows partitioning the union of two sets in the pointclass into two disjoint sets in the same pointclass
• Reduction (complexity), in computational complexity theory, the transformation of an instance of one problem into an instance of another
• Reduce computer algebra system, a general-purpose computer algebra system geared towards applications in physics.
• Reduce (higher-order function), a family of higher-order functions that process a data structure in some order and build up a return value.