Definition of a vector field on a differentiable manifold.

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Wikipedia defines the vector field at a point on a manifold to lie in its tangent space. But is this general enough? Consider a surface traction vector on some manifold, for example. It will have a component in the normal direction. Is this not considered a vector field then since it doesn't lie in the tangent space?

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Indeed, it is not a vector field on the surface, for the reason you wrote. Such a thing is called a vector field along the inclusion of the surface in the ambient manifold. What it basically means is that at any point on the surface there is a vector tangent to the ambient space (and not necessarily to the surface).

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More generally this could be described in terms of vector bundles,

A vector bundle ... makes precise the idea of a family of vector spaces parameterized by another space X ...: to every point x of the space X we associate (or "attach") a vector space V(x) ..., which is then called a vector bundle over X.

... and sections,

Essentially, a section assigns to every point ... a vector from the attached vector space, in a continuous manner.

https://en.wikipedia.org/wiki/Vector_bundle