What's thedifference between a bridge and a causeway?

Briefly, both are constructions for passing through or over water obstacles. The causeway goes through while the bridge goes over., . , https://en.wikipedia.org/wiki/Causeway . , . , https://en.wikipedia.org/wiki/Bridge

No, some bridges are supported from below. Think of the roman arched aqueducts that were bridges for water delivery. They applied the arch for many bridge structures in conjunction with causeways to build their roads which still exist in many places. More modern bridges take advantage of a greater knowledge of Physics to build suspension bridges, true.

"A transport corridor that is carried instead on a series of arches, perhaps approaching a bridge, is a viaduct. In the U.S. a short stretch of viaduct is called an overpass. The distinction between the terms causeway and viaduct becomes blurred when flood-relief culverts are incorporated, though generally a causeway refers to a roadway supported mostly by earth or stone, while a bridge supports a roadway between piers (which may be embedded in embankments)."

https://en.wikipedia.org/wiki/Causeway

"A bridge is a structure which allows passage over some type of impediment to travel (such as a roadway over a river, or other body of water). Anecdotally, causeways tend to refer to roadways which are close to the surface of the water or wetlands they provide passage over, and often do not allow nautical navigation underneath them."

http://www.answers.com/Q/What_is_difference_between_a_bridge_and_a_causeway

Just wondering because I read that Singapore has a bridge and a causeway(2 structures in total), which connect to Malaysia.

That's right. The causeway dates back quite a long time, and it breaks the flow of the water in the Straits of Johor, being a solid structure with its base on the sea bed. Malaysia would, I think, like to replace it with another bridge to enable ships to pass north of Singapore. I don't think Singapore is quite as keen. The bridge is fairly recent. https://en.wikipedia.org/wiki/Malaysia%E2%80%93Singapore_Second_Link https://en.wikipedia.org/wiki/Johor%E2%80%93Singapore_Causeway