  When the Mott insulating state is suppressed by charge carrier doping, the
pseudogap phenomenon emerges, where at the low-temperature limit,
superconductivity coexists with some ordered electronic states. Within the
framework of the kinetic-energy-driven superconductivity, the nature of the
pair-density-wave order in cuprate superconductors is studied by taking into
account the pseudogap effect. It is shown that the onset of the
pair-density-wave order does not produce an ordered gap, but rather a novel
hidden order as a result of the interplay of the charge-density-wave order with
superconductivity. As a consequence, this novel hidden pair-density-wave order
as a subsidiary order parameter coexists with the charge-density-wave order in
the superconducting-state, and is absent from the normal-state.
