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: 
computationalgeometry× 194
Using computers to solve geometric problems. Questions with this tag should typically have at least one other tag indicating what sort of geometry is involved, such as ag.algebraicgeometry or mg.metr…

convexoptimization× 193
Optimization with convex constraints and convex objectives; notions related to convex optimization such as subgradients, normal cones, separating hyperplanes

motives× 193  hodgetheory× 191 
stablehomotopy× 191  algebraicsurfaces× 190 
hilbertspaces× 188
a real or complex vector space endowed with an inner product such that $H$ is a complete metric space when endowed with the norm induced by this inner product.

characteristicp× 187 
birationalgeometry× 186 
teaching× 186
For questions related to teaching mathematics. For questions in Mathematics Education as a scientific discipline there is also the tag mathematicseducation. Note you may also ask your question on htt…

manifolds× 185 
riemannzetafunction× 180
the function of one complex variable $s$ defined by the series $\zeta(s) = \sum_{n \geq 1} \frac{1}{n^s}$ when $\operatorname{Re}(s)>1$. It admits a meromorphic continuati…

euclideangeometry× 178  randomwalk× 176 
textbookrecommendation× 175
Questions asking for recommendations of textbooks on some subject. It can be helpful to indicate whether the request is for selfstudy, for use in a course one teaches, for use accompanying a course o…

monoidalcategories× 174 
mathphilosophy× 170  eigenvalues× 165  groupactions× 165 
differentialoperators× 164
Elliptic, parabolic and hyperbolic operators. Laplace, LaplaceBeltrami, Schrödinger, Dirac. Exterior derivative and Lie derivative operators.

calculusofvariations× 162  semigroups× 162 
lfunctions× 158
Questions about generalizations of the Riemann Zeta function of arithmetic interest whose definition relies on meromorphic continuation of special kinds of Dirichlet series, such as Dirichlet Lfuncti…

prooftheory× 157
For question in Proof Theory, where "proofs" themselves are the object of mathematical investigation. It is not to be used to request a proof of some result.

spectralgraphtheory× 157
Questions related to the spectrum of graphs, defined using one of the possible variants of the discrete Laplace operator or Laplacian matrix.
See https://en.wikipedia.org/wiki/Discrete_Laplace_oper…

langlandsconjectures× 155
Higher reciprocity laws

computeralgebra× 155
Using computers to solve algebraic problems. Questions with this tag should typically include at least one other tag indicating what sort of algebraic problem is involved, such as ac.commutativealgeb…

graphcolorings× 153 
geometricmeasuretheory× 153
Questions about geometric properties of sets using measure theoretic techniques; rectifiability of sets and measures, currents, Plateau problem, isoperimetric inequality and related topics.

homology× 153  classfieldtheory× 151 
universalalgebra× 151
The study of algebraic structures and properties applying to large classes of such structures. For example, ideas from group theory and ring theory are extended and considered for structures with oth…

zetafunctions× 151  planegeometry× 150  intersectiontheory× 149  gm.generalmathematics× 147 