  Identifying the hidden organizational principles and relevant structures of
networks representing complex physical systems is fundamental to understand
their properties. To this aim, uncovering the structures involving a network's
prominent nodes in a network is an effective approach. In temporal networks,
the simultaneity of connections is crucial for temporally stable structures to
arise. We thus propose here a novel measure to quantitatively investigate the
tendency of well connected nodes to form simultaneous and stable structures in
a temporal network. We refer to this tendency, when observed, as the "temporal
rich club phenomenon". We illustrate the interest of this concept by analyzing
diverse data sets under this lens, and showing how it enables a new perspective
on their temporal patterns, from the role of cohesive structures in relation to
processes unfolding on top of the network to the study of specific moments of
interest in the evolution of the network.
