postulated topological structure in general relativity, where a space-time
"tunnel" links two distant points with a shortcut. Whether they can
be physically realized is not known, and they seem to require exotic matter to be stable. If they can exist, and can be built, they
could provide a possible way to travel faster than light (in a global sense,
since locally the travellers would move slower than light). For more
information, see Traversable Wormholes by Michael Clive Price.