We define a cylinder as the body generated by a rectangle that turns around one of its sides. The elements of the cylinder are:

The axis is the fixed side around which the rectangle turns.

The generator side is the side opposite to the axis that generates the cylinder.

The bases are the circles that generate the sides perpendicular to the axis.
 The height is the distance between two bases, this distance is equal to the sides.
We also have the oblique cylinder, which is when the axis is not perpendicular to the base.