Chemistry

• Reduction (chemistry), part of a reduction-oxidation (redox) reaction in which atoms have their oxidation state changed.
  • Organic redox reaction, a redox reaction that takes place with organic compounds
  • Ore reduction: see smelting

Computing and algorithms

• Reduction (complexity), a transformation of one problem into another problem
• Reduction (recursion theory), given sets A and B of natural numbers, is it possible to effectively convert a method for deciding membership in B into a method for deciding membership in A?
• Bit Rate Reduction, an audio compression method
• Data reduction, simplifying data in order to facilitate analysis
• Graph reduction, an efficient version of non-strict evaluation
• L-reduction, a transformation of optimization problems which keeps the approximability features
• Partial order reduction, a technique for reducing the size of the state-space to be searched by a model checking algorithm
• Strength reduction, a compiler optimization where a function of some systematically changing variable is calculated more efficiently by using previous values of the function
• Reduce (computer algebra system), a general-purpose computer algebra system geared towards applications in physics
• Reduce (higher-order function), in functional programming, a family of higher-order functions that process a data structure in some order and build up a return value
• Reduced instruction set computing, a CPU design philosophy favoring an instruction set reduced in size and complexity of addressing, to simplify implementation, instruction level parallelism, and compiling
• Reduction operator, a type of operator that is commonly used in parallel programming to reduce the elements of an array into a single result.

Pure mathematics and statistics

• Reducible as the opposite of irreducible (mathematics)
• Reduction (mathematics), the rewriting of an expression into a simpler form
• Beta reduction, the rewriting of an expression from lambda calculus into a simpler form
• Dimension reduction, the process of reducing the number of random variables under consideration
• Lattice reduction, given an integer lattice basis as input, to find a basis with short, nearly orthogonal vectors
• Subject reduction or preservation, a rewrite of an expression that does not change its type
• Reduction of order, a technique for solving second-order ordinary differential equations
• Reduction of the structure group, for a ${\displaystyle G}$-bundle ${\displaystyle B}$ and a map ${\displaystyle H\to G}$ an ${\displaystyle H}$-bundle ${\displaystyle B_{H}}$ such that the pushout ${\displaystyle B_{H}\times _{H}G}$ is isomorphic to ${\displaystyle B}$
• Reduction system, reduction strategy, the application of rewriting systems to eliminate reducible expressions
• Reduced form, in statistics, an equation which relates the endogenous variable X to all the available exogenous variables, both those included in the regression of interest (W) and the instruments (Z)
• Reduced homology, a minor modification made to homology theory in algebraic topology, designed to make a point have all its homology groups zero
• Reduced product, a construction that generalizes both direct product and ultraproduct
• Reduced residue system, a set of φ(n) integers such that each integer is relatively prime to n and no two are congruent modulo n
• Reduced ring, a ring with no non-zero nilpotent elements
• Reduced row echelon form, a certain reduced row echelon form of a matrix which completely and uniquely determines its row space
• Reduced word, in a free group, a word with no adjacent generator-inverse pairs
• Variance reduction, a procedure used to increase the precision of the estimates that can be obtained for a given number of iterations

Medicine

Physics

• Dimensional reduction, the limit of a compactified theory where the size of the compact dimension goes to zero
• Reduction criterion, in quantum information theory, a necessary condition a mixed state must satisfy in order for it to be separable
• Reduced mass, the "effective" inertial mass appearing in the two-body problem of Newtonian mechanics
• Reduced properties (pressure, temperature, or volume) of a fluid, defined based on the fluid's critical point

Other uses in science and technology

• Lithic reduction, in Stone Age toolmaking, to detach lithic flakes from a lump of tool stone
• Noise reduction, in acoustic or signal processing
• Reduction drive, a mechanical device to shift rotational speed