  Nuclear isomers are the metastable excited states of nuclei. The isomers can
be categorized into a few classes including spin, seniority, \emph{K}, shape
and fission isomers depending upon the hindrance mechanisms. In this paper, we
aim to present an overview of seniority isomers, which is a category related to
the seniority quantum number. The discussion is mainly based on the concepts of
seniority and generalized seniority. Various aspects of seniority isomers and
their whereabouts have been covered along with the situations where seniority
mixing prevents the isomerism.
