- K-connected graph
- K-edge-connected graph
- K-factor
- K-function
- K-homology
- K-map
- K-means clustering algorithm
- K-space
- K-subset
- K-theory or K-Theory
- K3 surface
- Kac-Moody algebra
- Kadomtsev-Petviashvili equation
- Kakeya needle problem
- Kakeya set
- Kakutani's fixed point theorem
- Kakutani's problem
- Kalman Filter or Kalman filter
- Kam theorem
- Kampyle of Eudoxus
- Kanizsa triangle
- Kantorovich inequality
- Kaplan-Yorke map
- Kappa
- Kappa curve
- Kaprekar constant
- Kaprekar number
- Kaprekar routine
- Karatsuba Multiplication or Karatsuba multiplication
- Karl Weierstraß
- Karnaugh Map or Karnaugh map
- Karush-Kuhn-Tucker conditions
- Kathleen Ollerenshaw or Kathleen ollerenshaw
- Kauffman polynomial
- Kautz graph
- Kazhdan-Lusztig polynomial or Kazhdan-lusztig polynomial
- Kei
- Keith number
- Kelvin function
- Kelvin Functions or Kelvin functions
- Kempe chain
- Kendall coefficient of rank correlation
- Kendall tau metric
- Kepler Conjecture or Kepler conjecture
- Kepler equation
- Kepler Problem or Kepler problem
- Kepler Solid or Kepler solid
- Kepler's Equation or Kepler's equation
- Kepler's problem
- Kepler-Poinsot solid or Kepler-poinsot solid
- Ker
- Kernel
- Kernel (category theory)
- Kernel function
- Kernel pair
- Kerr metric
- Ket
- Key
- Khinchin
- Khinchin constant
- Khinchin inequality
- Khinchin's constant
- Khinchin's inequality
- Khinchin's theorem
- Khinchin-Lévy constant
- Khintchine constant
- Kibibyte
- Killing form
- Killing vector
- Killing vectors
- Kilobyte
- King's graph
- Kinoshita-Terasaka knot
- Kirby calculus
- Kirby-Siebenmann invariant
- Kirkman's schoolgirl problem
- Kissing number
- Kite
- Kleene algebra
- Kleene star
- Kleene's recursion theorem
- Kleene's s-m-n Theorem
- Klein 4-group
- Klein bottle or Klein Bottle
- Klein curve
- Klein four-group
- Klein Quartic or Klein quartic
- Klein's absolute invariant
- Klein's modular function
- Klein-Beltrami model
- Klein-Erdos-Szekeres problem
- Klein-Gordon Equation or Klein-Gordon equation or Klein-gordon equation
- Kleinian group
- Kloosterman sum
- Kloosterman's sum
- Knapsack problem
- Knaster–Tarski theorem
- Kneser graph
- Kneser graphs
- Kneser theorem
- Knight's Tour or Knight's tour
- Knight's tour graph
- Knights of the Round Table or Knights of the round table
- Knot
- Knot complement
- Knot diagram
- Knot genus
- Knot group
- Knot invariant
- Knot polynomial
- Knot sum
- Knot theory or Knot Theory
- Knot vector
- Knudsen number
- Knuth's up arrow notation
- Knuth-Bendix algorithm
- Knuth-Bendix completion algorithm
- Knödel number
- Knödel numbers
- Koch curve
- Koch Island
- Koch snowflake
- Kodaira dimension
- Kodaira embedding theorem
- Koebe function
- Koethe conjecture
- Kolmogorov axiom
- Kolmogorov Complexity or Kolmogorov complexity
- Kolmogorov entropy
- Kolmogorov inequality
- Kolmogorov space
- Kolmogorov test
- Kolmogorov zero-one law
- Kolmogorov's axioms
- Kolmogorov's inequality
- Kolmogorov-Arnold-Moser Theorem or Kolmogorov-Arnold-Moser theorem
- Kolmogorov-Chapman equation or Kolmogorov-chapman equation
- Kolmogorov-Sinai entropy
- Kolmogorov-Smirnov test
- Kontorovich-Lebedev Transform or Kontorovich-Lebedev transform
- Korteweg-de Vries equation or Korteweg-de vries equation or Korteweg-de Vries Equation
- Koszul complex
- Krawtchouk polynomial
- Krawtchouk polynomials
- Krein space
- Krein-Milman theorem
- Krohn-Rhodes complexity
- Krohn-Rhodes Theorem or Krohn-Rhodes theorem
- Krohn-Rhodes Theory or Krohn-Rhodes theory
- Kronecker delta
- Kronecker product
- Kronecker symbol
- Kronecker theorem
- Kronecker's Jugendtraum or Kronecker's jugendtraum
- Kronecker-Weber theorem
- Kronecker’s limit formula
- Krull dimension
- Krull intersection theorem
- Krull's intersection theorem
- Krull's principal ideal theorem or Krull's Principal Ideal Theorem
- Krull-Remak-Schmidt theorem
- Krull-Schmidt theorem
- Kruskal's algorithm
- Kruskal's Tree Theorem or Kruskal's tree theorem
- Kruskal-Katona theorem
- Kruskal-Wallis test
- Krylov-Bogolubov theorem or Krylov-bogolubov theorem
- Krystyna Kuperberg
- KS Entropy
- Kuhn-Tucker conditions
- Kuhn-Tucker Theorem or Kuhn-Tucker theorem
- Kullback-Leibler Distance or Kullback-Leibler distance
- Kummer extension
- Kummer surface
- Kummer theory
- Kummer's function
- Kummer's series
- Kunihiko Kodaira
- Kupershmidt Equation or Kupershmidt equation
- Kuratowski's closure-complement problem
- Kuratowski's theorem
- Kurt Mahler or Kurt mahler
- Kurtosis
- Kurtosis excess
- Kynea number
- Kähler form
- Kähler manifold
- Kähler metric
- Kähler potential
- Kähler structure
- Kähler-Einstein manifold
- Kähler-Einstein metric
- Käte Fenchel
- Köbe function
- Köchel number
- König theorem
- König's lemma or König's Lemma
- König's theorem
- Königsberg bridge problem
- Künneth formula
