1. A four-wheeled, two-seated carriage with seats that face each other, with a two-section folding roof that meets in the middle of the passenger compartment.
2. An automobile with a folding top over the rear passenger compartment.
Lois Lane had one (the car, not the carriage), on the Superman TV series.
The British royal famly has multiple landau carriages, including one referred to as the 1902 State Landau.
It's also a relatively common surname; a German mathematician and a Russian physicist have lent the name to numerous mathematical and scientific terms.
Etymology: mid-1700s, from the town of Landau in Germany, where such carriages were first made.