These are the large rather round parts with the deep cooling fins on the outside. The I.D. bore is where the piston assemblies ride.
Cylinder machines are generally smaller and lighter than uprights. They make cleaning upholstery and awkward areas e.g. stairs, around furniture and inside cars easier. They are also ideal for use on hard floors.
Not actual engine components, but a mechanical sub-system of an engine compromising the piston and the cylindrical hole it moves in. Generally, the more cylinders an engine has the more power it develops and the more fuel it uses, but that's also dependent on the state of tuning, and the capacity of each cylinder.
in a steam locomotive the energy contained in steam is turned into mechanical force inside the cylinders. Each cylinder contains a piston and the pressure of the steam on the piston produces the force.