Part of the "Megastructures: The Visual Encyclopedia" book project, on sale now at http://www.neilblevins.com/megastructures/megastructures.htm
A Warp Gate would be a structure that would house the entrance to an artificial traversable wormhole, which is a distortion of space-time that provides instantaneous travel from one point to another in space, in time, or even between different dimensions. The gate would consist of two parts - one at the point of origin, and one at the destination.
Different sizes of gates could be constructed to allow for human travel through person-sized gates on a planet, or even objects the size of spacecraft through orbiting gates. Popular literature has even spoken of the possibility of giant gates large enough to transport a planet from one location to another.