A tag is a keyword or label that categorizes your question with other, similar questions. Using the right tags makes it easier for others to find and answer your question.
Type to find tags: 
ag.algebraicgeometry× 8479
Algebraic varieties, stacks, sheaves, schemes, moduli spaces, complex geometry, quantum cohomology.

nt.numbertheory× 5552
Prime numbers, Diophantine equations, analytic number theory, algebraic number theory, arithmetic geometry, Galois theory, transcendental number theory, continued fractions

referencerequest× 4301
used if a reference is needed in a paper or textbook on a specific result.

co.combinatorics× 3213
Enumerative combinatorics, graph theory, order theory, posets, matroids, designs and other discrete structures. It also includes algebraic, analytic and probabilistic combinatorics.

at.algebraictopology× 3131
Homotopy, stable homotopy, homology and cohomology, homotopical algebra.

gr.grouptheory× 3117
Questions about the branch of abstract algebra that deals with groups.

dg.differentialgeometry× 3004
Complex, contact, Riemannian, pseudoRiemannian and Finsler geometry, relativity, gauge theory, global analysis.

pr.probability× 2734
Theory and applications of probability and stochastic processes: e.g. central limit theorems, large deviations, stochastic differential equations, models from statistical mechanics, queuing theory.

fa.functionalanalysis× 2499
Banach spaces, function spaces, real functions, integral transforms, theory of distributions, measure theory.

rt.representationtheory× 2328
Linear representations of algebras and groups, Lie theory, associative algebras, multilinear algebra.

ct.categorytheory× 2258
Categories and functors, universal properties, algebras and algebraic theories, topoi, enriched and internal categories, structured categories (abelian, monoidal, etc), higher categories.

ac.commutativealgebra× 2043
Commutative rings, modules, ideals, homological algebra, computational aspects, invariant theory, connections to algebraic geometry and combinatorics.

linearalgebra× 1929
Questions about the properties of vector spaces and linear transformations, including linear systems in general.

lo.logic× 1861
firstorder and higherorder logic, model theory, set theory, proof theory, computability theory, formal languages, definability, interplay of syntax and semantics, constructive logic, intuitionism, p…

settheory× 1782
forcing, large cardinals, descriptive set theory, infinite combinatorics, cardinal characteristics, forcing axioms, ultrapowers, measures, reflection, pcf theory, models of set theory, axioms of set t…

graphtheory× 1733
Questions about the branch of combinatorics called graph theory (not to be used for questions concerning the graph of a function). This tag can be further specialized via using it in combination with …

gt.geometrictopology× 1490
Topology of cell complexes and manifolds, classification of manifolds (e.g. smoothing, surgery), low dimensional topology (e.g. knot theory, invariants of 4manifolds), embedding theory, combinatorial…

gn.generaltopology× 1403
Continuum theory, pointset topology, spaces with algebraic structure, foundations, dimension theory, local and global properties.

ca.analysisandodes× 1372
Special functions, orthogonal polynomials, harmonic analysis, ODE's, differential relations, calculus of variations, approximations, expansions, asymptotics.

ra.ringsandalgebras× 1120
Noncommutative rings and algebras, nonassociative algebras, universal algebra and lattice theory, linear algebra, semigroups.

softquestion× 1111
Questions that ask about some aspect of mathematical research or study which doesn't involve the actual mathematics. In general, soft questions can be answered without using mathematical reasoning.

mg.metricgeometry× 1102
Euclidean, hyperbolic, discrete, convex, coarse geometry, comparisons in Riemannian geometry, symmetric spaces.

ap.analysisofpdes× 1037
Existence and uniqueness, regularity, boundary conditions, linear and nonlinear operators, stability, soliton theory, integrable PDEs, conservation laws, qualitative dynamics.

complexgeometry× 974
the study of complex manifolds and complex algebraic varieties. It is a part of both differential geometry and algebraic geometry.

liegroups× 953
Groups that are additionally smooth manifolds such that the multiplication and the inverse maps are smooth.

matrices× 943
Questions where the notion matrix has an important or crucial role (for the latter, note the tag matrixtheory for potential use). Matrices appear in various parts of mathematics, and this tag is typi…

homotopytheory× 883  realanalysis× 846 
mp.mathematicalphysics× 838
Mathematical methods in quantum field theory, quantum mechanics, statistical mechanics, condensed matter, nuclear and atomic physics.

ds.dynamicalsystems× 818
Dynamics of differential equations and flows, mechanics, classical fewbody problems, iterations, complex dynamics, delayed differential equations.

measuretheory× 763
Questions about abstract measure and integral theory. Also concerns such properties as measurability of maps and sets.

homologicalalgebra× 758 
st.statistics× 745
Applied, computational and theoretical statistics: e.g. statistical inference, regression, time series, multivariate analysis, data analysis, Markov chain Monte Carlo, design of experiments, case stud…

cv.complexvariables× 738
Holomorphic functions, automorphic group actions and forms, pseudoconvexity, complex geometry, analytic spaces, analytic sheaves.

liealgebras× 684
algebraic structures which were introduced to study the concept of infinitesimal transformations. The term "Lie algebra" (after Sophus Lie) was introduced by Hermann Weyl in the 1930s…

algebraicgroups× 679 