  Understood in terms of pure states evolving into mixed states, the
possibility of information loss in black holes is closely related to the global
causal structure of spacetime, as is the existence of event horizons. However,
black holes need not be defined by event horizons, and in fact we argue that in
order to have a fully unitary evolution for black holes, they should be defined
in terms of something else, such as a trapping horizon. The Misner-Sharp mass
in spherical symmetry shows very simply how trapping horizons can give rise to
black hole thermodynamics, Hawking radiation and singularities. We show how the
Misner-Sharp mass can also be used to give insights into the process of
collapse and evaporation of locally defined black holes.
