A wormhole is a term for a theoretical bridge between two separate points in space. A wormhole could potentially connect distant stars allowing faster travel. If travel by conventional means took millions or billions of years, then using wormholes could cut that journey down to mere hours.
In Einstein's theory, he realized it was possible to construct a bridge between any two objects through curved spacetime. By manipulating these spaces, physicists can create routes, shortcuts, or portals.
The main problem with wormholes is that they need to have exotic matter to allow them to function properly. Even less is known about how this stuff works than regular matter.