A type of rumored clarketech device, never actually confirmed.
Some crypto-technologists have argued that since time and space are quantized (the Planck distance and Planck time, the smallest unit of either that can be measured), it might be possible to isolate a volume of space using metric engineering and then jump it 'out of phase' by one Planck time unit from the rest of the universe around it. The volume would then lag by one Planck unit of time behind everything else.
Since nothing can go backwards in time above the quantum level, a barrier or event horizon would appear to be created where the two regions interfaced. Nothing would be able to cross the barrier to enter the volume, although things could leave it since they would be going forward in time in the process. Alternatively, the volume in question might just seem to disappear without a trace.