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: 
tagremoved× 410
to be used only when retagging highly(!) offtopic questions where none of the actual tags would make sense; all actual tags the questioner has used are removed and something is needed to…

computabilitytheory× 410
computable sets and functions, Turing degrees, c.e. degrees, models of computability, primitive recursion, oracle computation, models of computability, decision problems, undecidability, Turing jump, …

kt.ktheoryhomology× 409
Algebraic and topological Ktheory, relations with topology, commutative algebra, and operator algebras

inequalities× 409 
forcing× 407
a method first used to prove the continuum hypothesis is independent of the classical axioms of set theory

convexpolytopes× 405
the convex hulls of a finite set of points in Euclidean spaces. They have rich combinatorial, arithmetic, and metrical theory, and are related to toric varieties and to linear pr…

terminology× 391
Questions of the kind "What's the name for a X that satisfies property Y?"

ergodictheory× 372
Dynamical systems on measure spaces, invariant measures, ergodic averages, mixing properties.

abelianvarieties× 367
projective algebraic varieties endowed with an Abelian group structure. Over the complex numbers, they can be described as quotients of a vector space by a lattice of full rank. …

sp.spectraltheory× 365
Schrodinger operators, operators on manifolds, general differential operators, numerical studies, integral operators, discrete models, resonances, nonselfadjoint operators, random operators/matrices…

computerscience× 363
For question borderline with, or having application to, computer science. Consider also posting http://cs.stackexchange.com/ or http://cstheory.stackexchange.com/ instead of here, if appropriate.

hyperbolicgeometry× 359 
simplicialstuff× 355  sheaftheory× 354  integration× 341 
geometricgrouptheory× 340
Large scale properties of groups; growth functions; Dehn functions; small cancellation properties; hyperbolicity and CAT(0); actions and representations; combinatorial group theory; presentations

groupcohomology× 339  examples× 336  galoistheory× 334 
openproblem× 330
equivalent to a known open problem, then the openproblem tag is added. After that, the question essentially becomes, "What is known about this problem? What are some…

convexgeometry× 329 
lattices× 327
used in number theory. (Not to be confused with lattice theory or lattices as used in physics!)

specialfunctions× 315
Many special functions appear as solutions of differential equations or integrals of elementary functions. Most special functions have relationships with representation theory of Lie groups.

diophantineequations× 310
polynomial equations $F=0$, or systems of polynomial equations $F_1=\ldots=F_k=0$, where $F,F_1,\ldots,F_k$ are polynomials in either $\mathbb{Z}[X_1,\ldots,X_n]$ of $\mathbb…

sobolevspaces× 307  convexity× 298  riemannsurfaces× 295  modelcategories× 295 
deformationtheory× 288 
stochasticcalculus× 286
Stochastic calculus provides a consistent theory of integration for stochastic processes and is used to model random systems. Its applications range from statistical physics to quantitative finance.

automorphicforms× 285 
cstaralgebras× 283
a complex Banach algebra together with an isometric antilinear involution satisfying (a b)* = b* a* and the C*identity ‖a* a‖ = ‖a‖². Related tags: [tag:banachalgebras], [tag:vonne…

asymptotics× 282  largecardinals× 280 
it.informationtheory× 279
Covers theoretical and experimental aspects of information theory and coding.

operatortheory× 276
Spectrum, resolvent, numerical range, functional calculus, operator semigroups. Special classes of operators: compact, Fredholm, dissipative, differential, integral, pseudodifferential, etc.
