  Motivated by the cosmological wormhole solutions obtained from our recent
numerical investigations, we provide a definition of a wormhole which applies
to dynamical situations. Our numerical solutions do not have timelike trapping
horizons but they are wormholes in the sense that they connect two or more
asymptotic regions. Although the null energy condition must be violated for
static wormholes, we find that it can still be satisfied in the dynamical
context. Two analytic solutions for a cosmological wormhole connecting two
Friedmann universes without trapping horizons are presented.
