A ro-ro is a ship that cars, trucks, and other vehicles can drive onto, and later drive off again. The name is short for “roll-on, roll-off”: the vehicles roll on at one port and roll off at the next. Car ferries are often ro-ro ships, and so are bigger cargo ships that carry hundreds of lorries. People in shipping use this word all the time; you will not hear it much in ordinary talk. It is the opposite idea from a ship where a crane lifts boxes on and off (in the trade that is “lo-lo”, lift-on lift-off). You write it ro-ro or Ro-Ro, and you say it like “roe-roe”, not letter by letter.