Quick answer
The bedding is the layer applied over the assembled cores and beneath the armour of an armoured cable. It is also called the inner sheath. Its job is to give the armour a smooth, even surface to sit on, so that the armour wires or strips do not press into the core insulation, and to fill the spaces between the cores so that the cable keeps a round, stable shape.
Without a bedding layer, the armour could bite into the insulation under bending, pulling or clamping loads. The inner and outer sheaths can be chosen to suit the installation, and APAR's LV XLPE cables offer PVC, PE, FR, FRLS or LSOH sheath options. The choice of armour itself is covered in the cable armouring guide.