This article reviews the concept of a tubular neighborhood. Intuitively, if S is a lower-dimensional smooth submanifold of an ambient m-dimensional smooth manifold M, then a tubular neighborhood of S is like a slightly thickened version of S, the union of sufficiently small m-dimensional neighborhoods of all the points in S. The precise definition uses the concept of a vector bundle over S, and the tubular neighborhood is equivalent to the total space of the bundle. A tubular neighborhood may be trivial or nontrivial. This article describes several examples.
