The tub holds the water; the drum or inner basket holds the laundry and allows water to pass through its perforations. The shaft, support, and bearings hold the moving assembly together according to its design.
Two containers with different jobs
In a system with an outer tub and an inner drum, the sealed container keeps the wash bath in place. The perforated drum exchanges water with it and moves the laundry along. During spin extraction, some of the water passes through the perforations and is drained from the lower circuit.
In horizontal-axis machines, the paddles lift the clothes during tumbling. In vertical-axis machines, the basket and the agitator or impeller take part depending on the design; the shape of the support cannot be inferred from the name drum or basket.
How the rotation is supported
The shaft connects the moving assembly to its drive. A support or spider can join it to the drum, while the bearings allow rotation and the sealing elements separate water from areas that must remain protected. Not all parts exist as separate replacement components.
The tub suspension serves a different purpose: it allows and limits movement of the assembly relative to the cabinet. A suspended tub can move without there being abnormal play between the drum and the support.
Materials and repairability
Steel and polymers may appear in different containers. Chemical resistance, geometry, joints, and operating conditions matter more than attributing an absolute advantage to a single material.
A tub may be removable or factory sealed; authorized repair depends on the parts breakdown. You should not assume it can be opened by cutting or that a material determines a specific service life.
Always distinguish what is moving: the drum inside the tub, or the whole assembly relative to the cabinet.