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× 8716
Algebraic varieties, stacks, sheaves, schemes, moduli spaces, complex geometry, quantum cohomology.

nt.numbertheory× 5710
Prime numbers, Diophantine equations, analytic number theory, algebraic number theory, arithmetic geometry, Galois theory, transcendental number theory, continued fractions

referencerequest× 4476
used if a reference is needed in a paper or textbook on a specific result.

co.combinatorics× 3346
Enumerative combinatorics, graph theory, order theory, posets, matroids, designs and other discrete structures. It also includes algebraic, analytic and probabilistic combinatorics.

at.algebraictopology× 3247
Homotopy, stable homotopy, homology and cohomology, homotopical algebra.

gr.grouptheory× 3212
Questions about the branch of abstract algebra that deals with groups.

dg.differentialgeometry× 3106
Complex, contact, Riemannian, pseudoRiemannian and Finsler geometry, relativity, gauge theory, global analysis.

pr.probability× 2830
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× 2615
Banach spaces, function spaces, real functions, integral transforms, theory of distributions, measure theory.

rt.representationtheory× 2402
Linear representations of algebras and groups, Lie theory, associative algebras, multilinear algebra.

ct.categorytheory× 2315
Categories and functors, universal properties, algebras and algebraic theories, topoi, enriched and internal categories, structured categories (abelian, monoidal, etc), higher categories.

ac.commutativealgebra× 2093
Commutative rings, modules, ideals, homological algebra, computational aspects, invariant theory, connections to algebraic geometry and combinatorics.

linearalgebra× 1993
Questions about the properties of vector spaces and linear transformations, including linear systems in general.

lo.logic× 1905
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× 1849
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× 1810
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× 1542
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× 1458
Continuum theory, pointset topology, spaces with algebraic structure, foundations, dimension theory, local and global properties.

ca.analysisandodes× 1399
Special functions, orthogonal polynomials, harmonic analysis, ODE's, differential relations, calculus of variations, approximations, expansions, asymptotics.

mg.metricgeometry× 1179
Euclidean, hyperbolic, discrete, convex, coarse geometry, comparisons in Riemannian geometry, symmetric spaces.

ra.ringsandalgebras× 1156
Noncommutative rings and algebras, nonassociative algebras, universal algebra and lattice theory, linear algebra, semigroups.

softquestion× 1136
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.

ap.analysisofpdes× 1092
Existence and uniqueness, regularity, boundary conditions, linear and nonlinear operators, stability, soliton theory, integrable PDEs, conservation laws, qualitative dynamics.

complexgeometry× 1017
the study of complex manifolds and complex algebraic varieties. It is a part of both differential geometry and algebraic geometry.

liegroups× 986
Groups that are additionally smooth manifolds such that the multiplication and the inverse maps are smooth.

matrices× 982
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× 917
an important subfield of algebraic topology. It is mainly concerned with the properties and structures of spaces which are invariant under homotopy. Chief among these are the homot…

realanalysis× 900 
mp.mathematicalphysics× 858
Mathematical methods in quantum field theory, quantum mechanics, statistical mechanics, condensed matter, nuclear and atomic physics.

ds.dynamicalsystems× 841
Dynamics of differential equations and flows, mechanics, classical fewbody problems, iterations, complex dynamics, delayed differential equations.

measuretheory× 791
Questions about abstract measure and integral theory. Also concerns such properties as measurability of maps and sets.

homologicalalgebra× 775 
cv.complexvariables× 773
Holomorphic functions, automorphic group actions and forms, pseudoconvexity, complex geometry, analytic spaces, analytic sheaves.

st.statistics× 749
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…

polynomials× 712
Questions in which polynomials (single or several variables) play a key role. It is typically important that this tag is combined with other tags; polynomials appear in very different contexts. Please…

oa.operatoralgebras× 710
Algebras of operators on Hilbert space, C^*algebras, von Neumann algebras, noncommutative geometry
