Supposedly a connection in a curved space-time between two areas, possibly very far from each other, that could allow matter and information to travel between them. Technically, could allow travelling between the two areas instantly or at timespan that appears as if the movement is much faster than the speed of light, without actually surpassing it due to the characteristics of the curved space time inside the wormhole (i.e. the distance between the two areas is much smaller inside the wormhole than it is outside of it).
Predicted as a possible phenomenon by the theory of general relativity, though as far as I know never observed or experimentally proven.
Doesn't needs to be manmade (and most likely isn't), could possibly connect between objects like a black hole and a white hole (the later an hypothetical object that could supposedly have the matter the falls into a black hole from one point at the universe being spilled out of it). Could be very fun if it was manmade as this could possibly allow traveling between very distant points at the universe, as if you were moving faster than light, without you actually do (so allowed by relativity).
Not really an expert at it but why not answering an unanswered question from two months ago. Hope that helps.
Edited by Aeon, 22 April 2017 - 03:32 PM.