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: 
ordertheory× 270  etalecohomology× 264  galoisrepresentations× 264  abstractalgebra× 262 
schemes× 262
the geometrical study of solutions of algebraic systems of equations, not only over the real/complex numbers, but also over integer numbers (and more generally o…

finitefields× 261  stacks× 261 
ellipticpde× 260
Questions about partial differential equations of elliptic type. Often used in combination with the toplevel tag ap.analysisofpdes.

topologicalgroups× 258 
randommatrices× 253
Statistics of spectral properties of matrixvalued random variables.

axiomofchoice× 251 
additivecombinatorics× 243
Questions on the subject additive combinatorics, also known as arithmetic combinatorics, such as questions on: additive bases, sum sets, inverse sum set theorems, sets with small doubling, Sidon sets,…

3manifolds× 243 
bigpicture× 242
Questions designed to get an overview of a specific subject or body of results or to understand the relations among similar definitions, techniques or concepts appearing in different subfields of mat…

derivedcategory× 241
For questions about the derived categories of various abelian categories and questions regarding the derived category construction itself.

fields× 241
Fields as algebraic objects. For vector and tensor fields, use eg. [dg.differentialgeometry]. For physical fields, use eg. [mp.mathematicalphysics] or [quantumfieldtheory].

singularitytheory× 240  modules× 238  quadraticforms× 236 
descriptivesettheory× 236
the study of definable subsets of Polish spaces, where definable is taken to mean from the Borel or projective hierarchies. Other topics include infinite games and determinac…

quantumgroups× 231
Questions about algebraic structures known as quantum groups, and their categories of representations. Quasitriangular Hopf algebras and their Drinfel'd twists, triangular Hopf algebras, $C^\star$ qua…

commutativerings× 230  projectivegeometry× 229 
intuition× 229
Questions asking for the intuition behind some definition, conjecture, proof etc. In other words, questions designed to improve or to acquire understanding on a conceptual or intuitive level, as oppos…

noncommutativealgebra× 228  topostheory× 228 
matrixanalysis× 226
The study of the properties of real and complex matrices that are more close to analysis and operator theory. For instance: the properties of positive definite matrices, matrix inequalities, perturbat…

linearprogramming× 225 
noncommutativegeometry× 224
Noncommutative geometry in the sense of Connes and beyond: noncommutative algebras viewed as functions on a noncommutative space.

vonneumannalgebras× 224
Subtag of [tag:oa.operatoralgebras] for questions about von Neumann algebras, that is, weak operator topology closed, unital, *subalgebras of bounded operators on a Hilbert space.

hopfalgebras× 218
a vector space $H$ over a field $k$ endowed with an associative product $\times:H\otimes_k H\to H$ and a coassociative coproduct $\Delta:H\to H\otimes_k H$ which is a morphism of alg…

algebraicktheory× 216 
mathematicseducation× 212
For questions in Mathematics Education as a scientific discipline. For more handson questions on teaching Mathematics, please use the tag teaching. There is also a Stack Exchange community http://mat…

approximationtheory× 209 
convexoptimization× 203
Optimization with convex constraints and convex objectives; notions related to convex optimization such as subgradients, normal cones, separating hyperplanes

markovchains× 202 