A cab is the part of a truck, tractor, or train engine where the driver sits to control the vehicle. The cab contains the steering wheel, pedals, dashboard, and seat, everything the driver needs to operate the machine safely. On a big semi-truck, the cab is that front section that looks almost like a small room, while the long trailer full of cargo stretches out behind it. On a farm tractor, the cab might be enclosed with windows and a roof to protect the driver from rain and sun, or it might be just a seat with a simple frame.

Modern train engines still use cab to describe where the engineer sits, even though trains run on tracks rather than roads.

The word cab also means a taxi, a car you can hire to take you somewhere. When someone says they'll “catch a cab” to the airport, they mean they'll hail a taxi. So whether you're talking about the driver's compartment in a vehicle or a taxi itself, you're using the word cab.