I have learned that there are white holes and black holes in the universe, but I am confused as to what a wormhole is. Is it a tunnel that connects black and white holes?
A wormhole is, in theory, a 'tunnel' which would be a shortcut to another point in spacetime. There's a Wikipedia article on the subject:
If you're the physicsy type, this might make some sense to you:
If this makes absolutely no sense to you, then you are just like me. Congratulations! For those that don't speak Greek math (such as me), here's an English explanation from space.com:
And here's a pretty picture of the effect:
A model of 'folded' space-time illustrates how a wormhole bridge might form with at least two mouths that are connected to a single throat or tube.
In plain English, it's a shortcut through spacetime, and the primary conceivable way time travel could happen.
A wormhole is a theorised phenomenon that would, if they exist, connect two different parts of space-time. A common analogy for the wormhole is to represent space-time as a two-dimensional sheet. If the two-dimensional sheet is bended over so that two points touch each other, than the point of contact becomes a wormhole. This has been suggested as a way to effectively travel faster than the speed of light (without actually travelling faster than the speed of light). As with most things, there are different theories about how a wormhole could exist and what its properties would be.