- Uban number
- UFD
- Ulam number
- Ulam sequence
- Ulam spiral
- Ulam's conjecture
- Ulam's problem
- Ulam's spiral
- Ultraconnected space
- Ultrafilter
- Ultrametric
- Ultrametric space
- Ultrametric triangle inequality
- Ultranet
- Ultranet (math)
- Ultrapower
- Ultraproduct
- Ultraradical
- Ultraspherical polynomial
- Ultraspherical polynomials
- Umbilic
- Umbilical point
- Umbral algebra
- Umbral calculus
- Umbrella
- Unambiguous
- Unar
- Unary operation
- Unbiased estimator
- Unbiased test
- Unbounded
- Unbounded operator
- Uncertainty principle
- Uncia
- Unconditional convergence
- Uncorrelated
- Uncountable set
- Uncountably infinite
- Undecagon
- Undecidability
- Undecidable
- Undecillion
- Undefined
- Underdamping
- Underdot
- Underscore
- Undetermined coefficients method
- Undirected graph
- Undulating number
- Unduloid
- Unexpected hanging paradox
- Unfair game
- Unfinished game
- Unhappy number
- Unicursal curve
- Unification
- Uniform algebra
- Uniform boundedness
- Uniform Boundedness Principle or Uniform boundedness principle
- Uniform Circular Motion or Uniform circular motion
- Uniform continuity
- Uniform convergence
- Uniform distribution
- Uniform distribution (continuous)
- Uniform expansivity
- Uniform great rhombicosidodecahedron
- Uniform great rhombicuboctahedron
- Uniform polychoron
- Uniform polyhedron
- Uniform space
- Uniform tessellation
- Uniform topology
- Uniformizable space
- Uniformization
- Uniformization theorem
- Uniformly Cauchy or Uniformly cauchy
- Uniformly continuous
- Uniformly distributed
- Uniformly equicontinuous
- Uniformly integrable
- Unilateral shift
- Unimodal
- Unimodal distribution
- Unimodular
- Unimodular group
- Unimodular lattice
- Unimodular matrix
- Union
- Union (set theory)
- Union of sets
- Union-closed set
- Union-closed sets conjecture
- Unipotent
- Unipotent element
- Unipotent group
- Unipotent matrix
- Unique
- Unique factorization
- Unique factorization domain
- Unique Factorization Theorem or Unique factorization theorem
- Unique prime
- Uniqueness theorem
- Unirational variety
- Unistable polyhedron
- Unit
- Unit ball
- Unit Cell or Unit cell
- Unit Circle or Unit circle
- Unit cube
- Unit disc
- Unit disk
- Unit element
- Unit fraction
- Unit interval
- Unit matrix
- Unit normal
- Unit ring
- Unit sphere
- Unit square
- Unit step
- Unit step function
- Unit vector
- Unit-distance graph
- Unital
- Unitarily equivalent
- Unitary
- Unitary dilation
- Unitary divisor
- Unitary group
- Unitary matrix
- Unitary operator
- Unitary perfect number
- Unitary representation
- Unitary space
- Unitary transformation
- Unity
- Univalent
- Univalent analytic function
- Univalent function
- Univariate
- Universal Algebra or Universal algebra
- Universal bundle
- Universal coefficient theorem
- Universal Cover or Universal cover
- Universal covering
- Universal covering space
- Universal derivation
- Universal enveloping algebra
- Universal function
- Universal graph
- Universal hash function
- Universal Product Code
- Universal property
- Universal quantifier
- Universal set
- Universal space
- Universal Turing Machine or Universal Turing machine or Universal turing machine
- Universality
- Universe
- Unknot
- Unknown
- Unless
- Unlink
- Unsolved problems
- Unsolved problems in mathematics
- Unstable fixed point
- Untouchable number
- Unusual number
- UPC or Upc
- Upper and lower bounds
- Upper bound or Upper Bound
- Upper half-plane
- Upper limit
- Upper set
- Upper sum
- Upper triangular matrix
- Upward Lowenheim-Skolem theorem
- Urchin
- Urelement
- Urn model
- Urn problem
- Urysohn function
- Urysohn lemma
- Urysohn metrization theorem
- Urysohn space
- Urysohn's lemma or Urysohn's Lemma
- Urysohn's metrization theorem
- Utility
- Utility theory
