This list of triangle topics includes things related to the geometric shape, either abstractly, as in idealizations studied by geometers, or in triangular arrays such as Pascal's triangle or triangular matrices, or concretely in physical space. It does not include metaphors like love triangle in which the word has no reference to the geometric shape.
See main article: Triangular array.
The (incomplete) Bell polynomials from a triangular array of polynomials (see also Polynomial sequence).