Glossary of differential geometry and topology

This is a glossary of terms specific to differential geometry and differential topology. The following three glossaries are closely related:

• Glossary of general topology
• Glossary of algebraic topology
• Glossary of Riemannian and metric geometry.

See also:

• List of differential geometry topics

Words in italics denote a self-reference to this glossary.

A

• Atlas

B

• Bundle – see fiber bundle.

• Basic element – A basic element $x$ with respect to an element $y$ is an element of a cochain complex $(C^{*},d)$ (e.g., complex of differential forms on a manifold) that is closed: $dx=0$ and the contraction of $x$ by $y$ is zero.

C

• Characteristic class
• Chart

• Cobordism

• Codimension – The codimension of a submanifold is the dimension of the ambient space minus the dimension of the submanifold.

• Connected sum

• Connection

• Cotangent bundle – the vector bundle of cotangent spaces on a manifold.

• Cotangent space
• Covering
• Cusp
• CW-complex

D

• Dehn twist
• Diffeomorphism – Given two differentiable manifolds $M$ and $N$, a bijective map $f$ from $M$ to $N$ is called a diffeomorphism – if both $f:M\to N$ and its inverse $f^{-1}:N\to M$ are smooth functions.
• Differential form
• Domain invariance

• Doubling – Given a manifold $M$ with boundary, doubling is taking two copies of $M$ and identifying their boundaries. As the result we get a manifold without boundary.

E

• Embedding
• Exotic structure – See exotic sphere and exotic ${ℝ}^4$.

F

• Fiber – In a fiber bundle, $\pi :E\to B$ the preimage ${\pi }^{-1}(x)$ of a point $x$ in the base $B$ is called the fiber over $x$, often denoted $E_x$.

• Fiber bundle

• Frame – A frame at a point of a differentiable manifold M is a basis of the tangent space at the point.

• Frame bundle – the principal bundle of frames on a smooth manifold.

• Flow

G

• Genus
• Germ
• Grassmannian bundle
• Grassmannian manifold

H

• Handle decomposition
• Hypersurface – A hypersurface is a submanifold of codimension one.

I

• Immersion

• Integration along fibers
• Irreducible manifold
• Isotopy

J

• Jet
• Jordan curve theorem

L

• Lens space – A lens space is a quotient of the 3-sphere (or (2n + 1)-sphere) by a free isometric action of Z – _k.
• Local diffeomorphism

M

• Manifold – A topological manifold is a locally Euclidean Hausdorff space (usually also required to be second-countable). For a given regularity (e.g. piecewise-linear, $C^k$ or $C^{\mathrm{\infty }}$ differentiable, real or complex analytic, Lipschitz, Hölder, quasi-conformal...), a manifold of that regularity is a topological manifold whose charts transitions have the prescribed regularity.
• Manifold with boundary
• Manifold with corners
• Mapping class group
• Morse function

N

• Neat submanifold – A submanifold whose boundary equals its intersection with the boundary of the manifold into which it is embedded.

O

• Orbifold
• Orientation of a vector bundle

P

• Pair of pants – An orientable compact surface with 3 boundary components. All compact orientable surfaces can be reconstructed by gluing pairs of pants along their boundary components.
• Parallelizable – A smooth manifold is parallelizable if it admits a smooth global frame. This is equivalent to the tangent bundle being trivial.
• Partition of unity
• PL-map

• Poincaré lemma

• Principal bundle – A principal bundle is a fiber bundle $P\to B$ together with an action on $P$ by a Lie group $G$ that preserves the fibers of $P$ and acts simply transitively on those fibers.

• Pullback

R

• Rham cohomology

S

• Section
• Seifert fiber space

• Submanifold – the image of a smooth embedding of a manifold.

• Submersion

• Surface – a two-dimensional manifold or submanifold.

• Systole – least length of a noncontractible loop.

T

• Tangent bundle – the vector bundle of tangent spaces on a differentiable manifold.

• Tangent field – a section of the tangent bundle. Also called a vector field.

• Tangent space

• Thom space

• Torus

• Transversality – Two submanifolds $M$ and $N$ intersect transversally if at each point of intersection p their tangent spaces $T_p(M)$ and $T_p(N)$ generate the whole tangent space at p of the total manifold.
• Triangulation

• Trivialization
• Tubular neighborhood

V

• Vector bundle – a fiber bundle whose fibers are vector spaces and whose transition functions are linear maps.

• Vector field – a section of a vector bundle. More specifically, a vector field can mean a section of the tangent bundle.

W

• Whitney sum – A Whitney sum is an analog of the direct product for vector bundles. Given two vector bundles $\alpha$ and $\beta$ over the same base $B$ their cartesian product is a vector bundle over $B\times B$. The diagonal map $B\to B\times B$ induces a vector bundle over $B$ called the Whitney sum of these vector bundles and denoted by $\alpha \oplus \beta$.
• Whitney topologies