**Sum** may refer to:

In mathematics:

- Summation, the addition of a sequence of numbers
- Addition, the elementary mathematical operations of arithmetic that totals amount of quantities combined
- Sum (category theory), the generic concept of summation in mathematics
- Additive and preadditive category
- Band sum, a way of connecting knots
- Connected sum, a way of gluing manifolds
- Digit sum, in number theory
- Direct sum, a combination of algebraic objects
- Einstein summation, a way of contracting tensor indecies
- Empty sum, a sum with no terms
- Fibered sum or pushout in category theory
- Indefinite sum, the inverse of a finite difference
- Matrix addition, in linear algebra
- QCD sum rules, in quantum field theory
- Power sum, in commutative algebra
- Prefix sum, in computing
- Riemann sum, in calculus
- Rule of sum in combinatorics
- Subset sum problem, in cryptography
- Sum rule in differentiation in calculus
- Sum rule in integration in calculus
- Sum rule in quantum mechanics
- Wedge sum, a one-point union of topological spaces
- Whitney sum of fiber bundles
- Zero-sum problem in combinatorics
- 3SUM, a term from computational complexity theory

In other areas:

- Sum, an old name for the Finns in East Slavic languages, derived from the word Suomi, "Finland"
*Sum: Forty Tales from the Afterlives*, a 2009 collection of short stories by David Eagleman- Sum (Unix), a program for generating checksums
- Sum (country subdivision), an administrative division in Mongolia and nearby regions
- the local term for one of the districts of Mongolia
- Som (currency), the unit of currency used in Turkic-speaking countries of Central Asia
- the IATA airport code for the Sumter Airport in Sumter County, South Carolina, USA
- the ISO 639-3 code for the Sumo language
- the first beat (pronounced like "some") in any rhythmic cycle of Hindustani classical music
- "Sum", a song by Pink Floyd from
*The Endless River*

As an acronym, **SUM** may refer to:

- Senter for utvikling og miljø (Centre for Development and the Environment), part of the University of Oslo
- SUM (interbank network)
- Soccer United Marketing
- The State University of Management, a Russian university

*Cogito ergo sum*- Sum 41, a Canadian punk band
- Sum certain, a legal term
- Cen (surname) sometimes romanized Sum