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: 
highercategorytheory× 462 
computabilitytheory× 449
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× 449
Algebraic and topological Ktheory, relations with topology, commutative algebra, and operator algebras

forcing× 446
a method first used to prove the continuum hypothesis is independent of the classical axioms of set theory

convexpolytopes× 444
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…

ergodictheory× 429
Dynamical systems on measure spaces, invariant measures, ergodic averages, mixing properties.

terminology× 428
Questions of the kind "What's the name for a X that satisfies property Y?"

sp.spectraltheory× 418
Schrodinger operators, operators on manifolds, general differential operators, numerical studies, integral operators, discrete models, resonances, nonselfadjoint operators, random operators/matrices…

integration× 417
Questions related to various forms of integration including the Riemann integral, Lebesgue integral, Riemann–Stieltjes integral, double integrals, line integrals, contour integrals, surface integrals,…

tagremoved× 409
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…

abelianvarieties× 403
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. …

hyperbolicgeometry× 394 
sheaftheory× 388 
computerscience× 385
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.

geometricgrouptheory× 383
Large scale properties of groups; growth functions; Dehn functions; small cancellation properties; hyperbolicity and CAT(0); actions and representations; combinatorial group theory; presentations

galoistheory× 382 
simplicialstuff× 380  groupcohomology× 377 
sobolevspaces× 368
a vector space of functions equipped with a norm that is a combination of Lpnorms of the function itself and its derivatives up to a given order.

convexgeometry× 363
A branch of geometry dealing with convex sets and functions. Polytopes, convex bodies, discrete geometry, linear programming, antimatroids, ...

specialfunctions× 354
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.

examples× 353 
openproblem× 352
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…

lattices× 352
used in number theory. (Not to be confused with lattice theory or lattices as used in physics!)

diophantineequations× 345
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…

stochasticcalculus× 342
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.

operatortheory× 336
Spectrum, resolvent, numerical range, functional calculus, operator semigroups. Special classes of operators: compact, Fredholm, dissipative, differential, integral, pseudodifferential, etc.

modelcategories× 332 
riemannsurfaces× 327 
cstaralgebras× 327
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…

deformationtheory× 320 
ellipticpde× 320
Questions about partial differential equations of elliptic type. Often used in combination with the toplevel tag ap.analysisofpdes.

convexity× 319  asymptotics× 314 
finitefields× 313
a field with a finite number of elements. For each prime power $q^k$, there is a unique (up to isomorphism) finite field with $q^k$ elements. Up to isomorphism, these are the only …

largecardinals× 312 